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rfc:rfc5413

Independent Submission P. Narasimhan Request for Comments: 5413 D. Harkins Category: Historic S. Ponnuswamy ISSN: 2070-1721 Aruba Networks

                                                         February 2010
             SLAPP: Secure Light Access Point Protocol

Abstract

 The Control and Provisioning of Wireless Access Points (CAPWAP)
 problem statement describes a problem that needs to be addressed
 before a wireless LAN (WLAN) network designer can construct a
 solution composed of Wireless Termination Points (WTP) and Access
 Controllers (AC) from multiple, different vendors.  One of the
 primary goals is to find a solution that solves the interoperability
 between the two classes of devices (WTPs and ACs) that then enables
 an AC from one vendor to control and manage a WTP from another.
 In this document, we present a protocol that forms the common
 technology-independent framework and the ability to negotiate and
 add, on top of this framework, a control protocol that contains a
 technology-dependent component to arrive at a complete solution.  We
 have also presented two such control protocols -- an 802.11 Control
 protocol, and another, more generic image download protocol, in this
 document.
 Even though the text in this document is written to specifically
 address the problem stated in RFC 3990, the solution can be applied
 to any problem that has a controller (equivalent to the AC) managing
 one or more network elements (equivalent to the WTP).

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for the historical record.
 This document defines a Historic Document for the Internet community.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.

Narasimhan, et al. Historic [Page 1] RFC 5413 SLAPP February 2010

 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5413.

IESG Note

 This RFC documents the SLAPP protocol as it was when submitted to the
 IETF as a basis for further work in the CAPWAP Working Group, and
 therefore it may resemble the CAPWAP protocol specification in RFC
 5415 as well as other IETF work.  This RFC is being published solely
 for the historical record.  The protocol described in this RFC has
 not been thoroughly reviewed and may contain errors and omissions.
 RFC 5415 documents the standards track solution for the CAPWAP
 Working Group and obsoletes any and all mechanisms defined in this
 RFC.  This RFC is not a candidate for any level of Internet Standard
 and should not be used as a basis for any sort of Internet
 deployment.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http//:trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.

Narasimhan, et al. Historic [Page 2] RFC 5413 SLAPP February 2010

Table of Contents

 1. Introduction ....................................................4
 2. Definitions .....................................................7
    2.1. Conventions Used in This Document ..........................7
 3. Topology ........................................................7
 4. Protocol ........................................................8
    4.1. Protocol Description .......................................8
         4.1.1. State Machine Explanation ...........................9
    4.2. Format of a SLAPP Header ..................................10
    4.3. Version ...................................................11
    4.4. Retransmission ............................................12
    4.5. Discovery .................................................12
         4.5.1. SLAPP Discover Request .............................13
         4.5.2. SLAPP Discover Response ............................15
    4.6. SLAPP Discovery Process ...................................17
         4.6.1. WTP ................................................17
         4.6.2. AC .................................................19
 5. Security Association ...........................................19
    5.1. Example Authentication Models (Informative) ...............20
         5.1.1. Mutual Authentication ..............................20
         5.1.2. WTP-Only Authentication ............................21
         5.1.3. Anonymous Authentication ...........................21
 6. SLAPP Control Protocols ........................................21
    6.1. 802.11 Control Protocol for SLAPP .........................21
         6.1.1. Supported CAPWAP Architectures .....................21
         6.1.2. Transport ..........................................24
         6.1.3. Provisioning and Configuration of WTP ..............26
         6.1.4. Protocol Operation .................................60
    6.2. Image Download Protocol ...................................66
         6.2.1. Image Download Packet ..............................66
         6.2.2. Image Download Request .............................67
         6.2.3. Image Download Process .............................68
         6.2.4. Image Download State Machine .......................69
 7. Security Considerations ........................................73
 8. Extensibility to Other Technologies ............................73
 9. Informative References .........................................74

Narasimhan, et al. Historic [Page 3] RFC 5413 SLAPP February 2010

1. Introduction

 The need for a protocol by which wireless LAN (WLAN) Access
 Controllers (ACs) can control and manage Wireless Termination Points
 (WTPs) from a different vendor has been presented in the CAPWAP
 problem statement [3].  We believe that this problem is more general
 than as stated in [3] and can be found in any application, including
 non-wireless ones, that requires a central controller to control and
 manage one or more network elements from a different vendor.
 One way to solve the CAPWAP problem is to define a complete control
 protocol that enables an AC from one vendor to control and manage a
 WTP from a different vendor.  But a solution that is primarily
 focused towards solving the problem for one particular underlying
 technology (IEEE 802.11, in this case) may find it difficult to
 address other underlying technologies.  Different underlying
 technologies may differ on the set of configurable options, and
 different architectural choices that are specific to that underlying
 technology (similar to the Local Medium Access Control (MAC) versus
 Split MAC architectures in 802.11).  The architectural choices that
 are good for one underlying technology may not necessarily work for
 another.  Not to forget that there may be multiple architectural
 choices [2] even for the same underlying technology.  A monolithic
 control protocol that strives to solve this problem for multiple
 technologies runs the risk of adding too much complexity and not
 realizing the desired goals, or it runs the risk of being too rigid
 and hampering technological innovation.
 A different way to solve this problem is to split the solution space
 into two components -- one that is technology-agnostic or
 independent, and another that is specific to the underlying
 technology or even different approaches to the same underlying
 technology.  The technology-independent component would be a common
 framework that would be an important component of the solution to
 this class of problems without any dependency on the underlying
 technology (i.e., 802.11, 802.16, etc.) being used.  The technology-
 specific component would be a control protocol that would be
 negotiated using this common framework and can be easily defined to
 be relevant to that technology without the need for having any
 dependency on other underlying technologies.  This approach also
 lends itself easily to extend the solution as new technologies arise
 or as new innovative methods to solve the same problem for an
 existing technology present themselves in the future.
 In this document, we present secure light access point protocol
 (SLAPP), a technology-independent protocol by which network elements
 that are meant to be centrally managed by a controller can discover
 one or more controllers, perform a security association with one of

Narasimhan, et al. Historic [Page 4] RFC 5413 SLAPP February 2010

 them, and negotiate a control protocol that they would use to perform
 the technology-specific components of the control and provisioning
 protocol.  We have also presented two control protocols in this
 document -- an 802.11 control protocol for provisioning and managing
 a set of 802.11 WTPs, and an image download protocol that is very
 generic and can be applied to any underlying technology.
 Figure 1 shows the model by which a technology-specific control
 protocol can be negotiated using SLAPP to complete a solution for a
 certain underlying technology.  The figure shows a control protocol
 for 802.11 and 802.16 technology components, but the SLAPP model does
 not preclude multiple control protocols within a certain technology
 segment.  For example, a certain technology-specific control protocol
 may choose to support only the Local MAC architecture [2] while
 deciding not to support the Split MAC architecture [2].  While the
 image download protocol is presented in this document, a SLAPP
 implementation MUST NOT assume that this control protocol is
 supported by other SLAPP implementations.

Narasimhan, et al. Historic [Page 5] RFC 5413 SLAPP February 2010

                                            Negotiated
          SLAPP                             Control
                                            Protocol
 +-------------------------+              +------------+
 |                         |              |            |
 |         SLAPP           |              |  Image     |
 | (technology-independent +-------+----->|  Download  |
 |      framework)         |       |      |  protocol  |
 |                         |       |      |            |
 |  negotiate one control  |       |      +------------+
 |  protocol here          |       |
 +-------------------------+       |
                                   |      +------------+
                                   |      |            |
                                   |      |   802.11   |
                                   +----->|  control   |
                                   |      |  protocol  |
                                   |      |            |
                                   |      +------------+
                                   |
                                   |
                                   |      +------------+
                                   |      |            |
                                   |      |   802.16   |
                                   +----->|  control   |
                                   |      |  protocol  |
                                   |      |            |
                                   |      +------------+
                                   |
                                   |         .......
                    Figure 1: SLAPP Protocol Model
 The control protocols that are negotiable using SLAPP are expected to
 be published ones that have gone through a review process in
 standards bodies such as the IETF.  The control protocols can either
 re-use the security association created during SLAPP or have the
 option of clearing all SLAPP state and restarting with whatever
 mechanisms are defined in the control protocol.
 Recently, there was a significant amount of interest in a similar
 problem in the Radio Frequency Identification (RFID) space that has
 led to the definition of a simple lightweight RFID reader protocol
 (SLRRP) [9].  It is quite possible that SLRRP could be a
 technology-specific (RFID, in this case) control protocol negotiated
 during a common technology-independent framework.

Narasimhan, et al. Historic [Page 6] RFC 5413 SLAPP February 2010

 All of the text in the document would seem to be written with a WLAN
 problem in mind.  Please note that while the letter of the document
 does position the solution to solve a CAPWAP-specific problem, the
 spirit of the document is to address the more general problem.

2. Definitions

2.1. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [1].

3. Topology

 The SLAPP protocol supports multiple topologies for interconnecting
 WTPs and ACs as indicated in Figure 2.
 In Figure 2, we have captured four different interconnection
 topologies:
 1.  The WTP is directly connected to the AC without any intermediate
     nodes.  Many WTPs are deployed in the plenum of buildings and are
     required to be powered over the Ethernet cable that is connecting
     it to the network.  Many ACs in the marketplace can supply power
     over Ethernet, and in the case where the AC is the one powering
     the WTP, the WTP is directly connected to the AC.
 2.  The WTP is not directly connected to the AC, but both the AC and
     the WTP are in the same Layer 2 (L2) (broadcast) domain.
 3.  The WTP is not directly connected to the AC, and they are not
     present in the same L2 (broadcast) domain.  They are on two
     different broadcast domains and have a node on the path that
     routes between two or more subnets.
 4.  The fourth case is a subset of the third one with the exception
     that the intermediate nodes on the path from the WTP to the AC
     may not necessarily be in the same administrative domain.  The
     intermediate network may also span one or more WAN links that may
     have lower capacity than if both the AC and the WTP are within
     the same building or campus.

Narasimhan, et al. Historic [Page 7] RFC 5413 SLAPP February 2010

             +-----------------+            +-------+
             |                 |    (1)     |       |
             |       AC        +------------+  WTP  |
             |                 |            |       |
             +--------+--------+            +-------+
                      |
                      |
                      |
                  +---+---+
             (2)  |       |
           +------+  L2   +--------+
           |      |       |        |
           |      +---+---+        |
           |                       |
           |                       |
     +-----+-----+             +---+---+    +-------+
     |           |             |       | (3)|       |
     |    WTP    |             |   L3  +----+  WTP  |
     |           |             |       |    |       |
     +-----------+             +---+---+    +-------+
                                   |
                                   |
                                   |
                               +---+----+    +-------+
                               |        | (4)|       |
                               |Internet+----+  WTP  |
                               |        |    |       |
                               +--------+    +-------+
                         Figure 2: SLAPP Topology

4. Protocol

4.1. Protocol Description

 The SLAPP state machine for both the WTP and AC is shown in Figure 3.
 Both the WTP and the AC discover each other, negotiate a control
 protocol, perform a secure handshake to establish a secure channel
 between them, and then use that secure channel to protect a
 Negotiated Control Protocol.
 The WTP maintains the following variable for its state machine:
 abandon: a timer that sets the maximum amount of time the WTP will
    wait for an acquired AC to begin the Datagram Transport Layer
    Security (DTLS) handshake.

Narasimhan, et al. Historic [Page 8] RFC 5413 SLAPP February 2010

    /--------\  /-----------\
    |        |  |           |
    |        v  v           |
    |  +-------------+      |
    | C| discovering |<-\   |
    |  +-------------+  |   |
    |        |          |   |
    |        v          |   |
    |  +-----------+    |   |
    \--| acquiring |    |   |
       +-----------+    |   |
             |          |   |
             v          |   |
       +----------+     |   |
      C| securing |-----/   |
       +----------+         |
             |              |
             v              |
     +----------------+     |
     |  negotiated    |     |
    C|    control     |-----/
     |   protocol     |
     +----------------+
                      Figure 3: SLAPP State Machine

4.1.1. State Machine Explanation

 Note: The symbol "C" indicates an event that results in the state
 remaining the same.
 Discovering
    AC: This is a quiescent state for the AC in which it waits for
        WTPs to request its acquisition.  When a request is received,
        the AC transitions to Acquiring.
   WTP: The WTP is actively discovering an AC.  When the WTP receives
        a response to its Discover Request, it transitions to
        Acquiring.
 Acquiring
    AC: A discover request from a WTP has been received.  If the
        request is invalid or the AC wishes to not acquire the WTP, it
        drops the packet and transitions back to Discovering.
        Otherwise, a Discover Response is sent and the AC transitions
        to Securing.

Narasimhan, et al. Historic [Page 9] RFC 5413 SLAPP February 2010

   WTP: A discover response from an AC has been received.  If the
        response is not valid, the WTP transitions to Discovering;
        otherwise, it sets the abandon timer to a suitable value to
        await a DTLS exchange.  If the timer fires in Acquiring, the
        WTP transitions back to Discovering.  If a DTLS "client hello"
        is received, the WTP transitions to Securing and cancels the
        abandon timer.
 Securing
    AC: The AC performs the "client end" of the DTLS exchange.  Any
        error in the DTLS exchange results in the AC transitioning to
        Discovering.  When the DTLS exchange finishes, the AC
        transitions to the Negotiated Control Protocol.
   WTP: The WTP performs the "server end" of the DTLS exchange.  Any
        error in the DTLS exchange results in the WTP transitioning to
        Discovering.  When the DTLS exchange finishes, the WTP
        transitions to the Negotiated Control Protocol.
 Negotiated Control Protocol
    AC: The AC performs its side of the protocol agreed to during the
        discovery process.  Please refer to Section 6.1 for the SLAPP
        802.11 Control Protocol.  For the Image Download Protocol
        example, see Section 6.2.
   WTP: The WTP performs its side of the protocol agreed to during the
        discovery process.  Please refer to Section 6.1 for the SLAPP
        802.11 Control Protocol.  For the Image Download Protocol
        example, see Section 6.2.

4.2. Format of a SLAPP Header

 All SLAPP packets begin with the same header as shown in Figure 4.
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  Maj  |  Min  |     Type      |           Length              |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        Figure 4: SLAPP Header
 Where:
    Maj (4 bits): the major number of the SLAPP version

Narasimhan, et al. Historic [Page 10] RFC 5413 SLAPP February 2010

    Min (4 bits): the minor number of the SLAPP version
    Type (1 octet): the type of SLAPP message
    Length (two octets): the length of the SLAPP message, including
    the entire SLAPP header
 The following types of SLAPP messages have been defined:
    name                     type
    -----                   ------
    discover request           1
    discover response          2
    image download control     3
    control protocol packet    4
    reserved                  5-255

4.3. Version

 SLAPP messages include a version in the form of major.minor.  This
 document describes the 1.0 version of SLAPP, that is the major
 version is one (1) and the minor version is zero (0).
 Major versions are incremented when the format of a SLAPP message
 changes or the meaning of a SLAPP message changes such that it would
 not be properly parsed by an older, existing version of SLAPP.  Minor
 versions are incremented when some incremental additions have been
 made to SLAPP that enhance its capabilities or convey additional
 information in a way that does not change the format or meaning of
 the SLAPP message.
 Future versions of SLAPP MAY NOT mandate support for earlier major
 versions of SLAPP, so an implementation MUST NOT assume that a peer
 that supports version "n" will therefore support version "n - i"
 (where both "n" and "i" are non-zero integers and "n" is greater than
 "i").
 A SLAPP implementation that receives a SLAPP message with a higher
 major version number MUST drop that message.  A SLAPP implementation
 that receives a SLAPP message with a lower major version SHOULD drop
 down to the version of SLAPP the peer supports.  If that version of
 SLAPP is not supported, the message MUST be dropped.  However, there
 may be valid reasons for which a peer wishes to drop a SLAPP message
 with a supported major version.
 A SLAPP implementation that receives a SLAPP message with a higher
 minor version number MUST NOT drop that message.  It MUST respond
 with the minor version number that it supports and will necessarily

Narasimhan, et al. Historic [Page 11] RFC 5413 SLAPP February 2010

 not support whatever incremental capabilities were added that
 justified the bump in the minor version.  A SLAPP implementation that
 receives a SLAPP message with a lower minor version MUST NOT drop
 that message.  It SHOULD revert back to the minor version that the
 peer supports and not include any incremental capabilities that were
 added that justified the bump in the minor version.

4.4. Retransmission

 SLAPP is a request response protocol.  Discovery and security
 handshake requests are made by the WTP, and responses to them are
 made by the AC.  Image Download packets are initiated by the AC and
 acknowledged by the WTP (in a negative fashion, see Section 6.2).
 Retransmissions are handled solely by the initiator of the packet.
 After each packet for which a response is required is transmitted,
 the sender MUST set a retransmission timer and resend the packet upon
 its expiry.  The receiver MUST be capable of either regenerating a
 previous response upon receipt of a retransmitted packet or caching a
 previous response and resending upon receipt of a retransmitted
 packet.
 The retransmission timer MUST be configurable and default to one (1)
 second.  No maximum or minimum for the timer is specified by this
 version of SLAPP.
 Each time a retransmission is made, a counter SHOULD be incremented,
 and the number of retransmissions attempted by a sender before giving
 up and declaring a SLAPP failure SHOULD be four (4)-- that is, the
 number of attempts made for each packet before declaring failure is
 five (5).
 The exception to this rule is Image Download packets, which are not
 individually acknowledged by the WTP (see Section 6.2).  The final
 packet is acknowledged and lost packets are indicated through Image
 Download Requests.

4.5. Discovery

 When a WTP boots up and wants to interoperate with an Access
 Controller so that it can be configured by the AC, one of the first
 things it needs to do is to discover one or more ACs in its network
 neighborhood.  This section contains the details of this discovery
 mechanism.
 As described in Section 3, an AC and a WTP could reside in the same
 Layer 2 domain, or be separated by a Layer 3 cloud including
 intermediate clouds that are not under the same administrative domain

Narasimhan, et al. Historic [Page 12] RFC 5413 SLAPP February 2010

 (for example, an AC and a WTP separated by a wide-area public
 network).  So any proposed discovery mechanism should have provisions
 to enable a WTP to discover an AC across all these topologies.
 We assume that a WTP, prior to starting the discovery process, has
 already obtained an IP address on its wired segment.

4.5.1. SLAPP Discover Request

 The SLAPP discovery process is initiated by sending a SLAPP discover
 request packet.  The packet can be addressed to the broadcast IP
 address, a well-known multicast address, or (if the IP address of an
 AC is either configured prior to the WTP booting up or is learned
 during the boot-up sequence) addressed to a unicast IP address.  Lack
 of a response to one method of discovery SHOULD result in the WTP
 trying another method of discovery.  The SLAPP discover request
 packet is a UDP packet addressed to port [TBD] designated as the
 SLAPP discovery port.  The source port can be any random port.  The
 payload of the SLAPP discover request packet is shown in Figure 5.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |    Type = 1   |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Transaction ID                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         WTP Identifier                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    WTP Identifier (continued) |             Flags             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      WTP Vendor ID                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      WTP HW Version                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      WTP SW Version                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | n controltypes| control type  |  .  .  .
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 5: SLAPP Discover Request

4.5.1.1. Transaction ID

 The transaction ID is a randomly generated, 32-bit number that is
 maintained during one phase of the SLAPP discovery process.  It is
 generated by a WTP starting a discovery process.  When one discovery
 method fails to find an AC and the WTP attempts another discovery

Narasimhan, et al. Historic [Page 13] RFC 5413 SLAPP February 2010

 method it MUST NOT re-use the Transaction ID.  All ACs that intend to
 respond to a SLAPP discover request must use the same value for this
 field as in the request frame.

4.5.1.2. WTP Identifier

 This field allows the WTP to specify a unique identifier for itself.
 This MAY be, for instance, its 48-bit MAC address or it could be any
 other string such as a serial number.

4.5.1.3. Flags

 The Flags field is used to indicate certain things about the discover
 request.  For example, bit 0 in the Flags field indicates whether the
 discover request packet is being sent to the AC, if unicast, based on
 a configuration at the WTP or based on some other means of discovery.
 This bit should always be set to the discover mode if the SLAPP
 discover request packet is being sent to either a broadcast or
 multicast address.  Here are the valid values for various bits in the
 Flags field.
    Bit 0:
    0 - Configuration mode
    1 - Discover mode
    Bits 1-15:
    Must always be set to 0 by the transmitter
    Must be ignored by the receiver

4.5.1.4. WTP Vendor ID

 This 32-bit field is the WTP vendor's Structure of Management
 Information (SMI) enterprise code in network octet order (these
 enterprise codes can be obtained from, and registered with, IANA).

4.5.1.5. WTP HW Version

 This 32-bit field indicates the version of hardware present in the
 WTP.  This is a number that is totally left to the WTP vendor to
 choose.

4.5.1.6. WTP SW Version

 This 32-bit field indicates the version of software present in the
 WTP.  This is a number that is totally left to the WTP vendor to
 choose.

Narasimhan, et al. Historic [Page 14] RFC 5413 SLAPP February 2010

4.5.1.7. Number of Control Types

 This 8-bit field indicates the number of 8-bit control protocol
 indicators that follow it and therefore implicitly indicates the
 number of different control protocols the WTP is capable of
 supporting.  This number MUST be at least one (1).

4.5.1.8. Control Types

 This 8-bit field indicates the type of control protocol the WTP
 supports and is willing to use when communicating with an AC.  There
 MAY be multiple "control type" indicators in a single SLAPP Discover
 Request.
    Valid Control Types
    -------------------
    0      - RESERVED (MUST not be used)
    1      - Image Download Control Protocol
    2      - 802.11 SLAPP Control Protocol
    3-255  - RESERVED (to IANA)

4.5.2. SLAPP Discover Response

 An AC that receives a SLAPP discover request packet from a WTP can
 choose to respond with a SLAPP discover response packet.  The format
 of the SLAPP discover response packet is shown in Figure 6.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |    Type = 2   |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Transaction ID                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        WTP Identifier                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    WTP Identifier (continued) |             Flags             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      AC HW Vendor ID                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       AC HW Version                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       AC SW Version                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | control type  |
 +-+-+-+-+-+-+-+-+
                   Figure 6: SLAPP Discover Response

Narasimhan, et al. Historic [Page 15] RFC 5413 SLAPP February 2010

 The SLAPP discover response packet is a UDP packet.  It is always
 unicast to the WTP's IP address.  The source IP address is that of
 the AC sending the response.  The source port is the SLAPP discover
 port [TBD] and the destination port is the same as the source port
 used in the SLAPP discover request.  The WTP's MAC address and the
 transaction ID must be identical to the values contained in the SLAPP
 discover request.  The Status field indicates to the WTP whether the
 AC is either accepting the discover request and is willing to allow
 the WTP to proceed to the next stage (ACK) or whether it is denying
 the WTP's earlier request (NACK).  The AC includes its own vendor ID,
 hardware, and software versions in the response.

4.5.2.1. Transaction ID

 The value of the Transaction ID field should be identical to its
 value in the SLAPP discover request packet sent by the WTP.

4.5.2.2. WTP Identifier

 The WTP Identifier that was sent in the corresponding SLAPP discover
 request frame.

4.5.2.3. Flags

 This field is unused by this version of SLAPP.  It MUST be set to
 zero (0) on transmission and ignored upon receipt.

4.5.2.4. AC Vendor ID

 If the value of the Status field is a 1, indicating that the AC is
 sending a successful response, then the values in this field and the
 following two are valid.  The 32-bit AC Vendor ID points to the
 vendor ID of the AC.  If the value of the Status field is not 1, then
 this field should be set to 0 by the AC and ignored by the WTP.

4.5.2.5. AC HW Version

 If the value of the Status field is 1, then this 32-bit field
 contains the value of the AC's hardware version.  This value is
 chosen by the AC vendor.  If the value of the Status field is not 1,
 then this field should be set to 0 by the AC and ignored by the WTP.

4.5.2.6. AC SW Version

 If the value of the Status field is 1, then this 32-bit field
 contains the value of the AC's software version.  This value is
 chosen by the AC vendor.  If the value of the Status field is not 1,
 then this field should be set to 0 by the AC and ignored by the WTP.

Narasimhan, et al. Historic [Page 16] RFC 5413 SLAPP February 2010

4.5.2.7. Control Type

 The control type that the AC will use to communicate with the WTP.
 This value MUST match one of the control types passed in the
 corresponding SLAPP Discover Request.

4.6. SLAPP Discovery Process

4.6.1. WTP

 There are multiple ways in which a WTP can discover an AC.
 1.  Static configuration: An administrator, prior to deploying a WTP,
     can configure an IP address of an AC on the WTP's non-volatile
     memory.  If this is the case, then the SLAPP discover request
     packet is addressed to the configured IP address.
 2.  DHCP options: As part of the DHCP response, the DHCP server could
     be configured to use option 43 to deliver the IP address of an AC
     to which the WTP should address the SLAPP discover request
     packet.  If the IP address of an AC is handed to the WTP as part
     of the DHCP response, then the WTP should address the SLAPP
     discover request packet to this IP address.
 3.  DNS configuration: Instead of configuring a static IP address on
     the WTP's non-volatile memory, an administrator can configure a
     Fully-Qualified Domain Name (FQDN) of an AC.  If the FQDN of an
     AC is configured, then the WTP queries its configured DNS server
     for the IP address associated with the configured FQDN of the AC.
     If the DNS query is successful and the WTP acquires the IP
     address of an AC from the DNS server, then the above discover
     request packet is addressed to the unicast address of the AC.
 4.  Broadcast: The WTP sends a discover request packet addressed to
     the broadcast IP address with the WTP's IP address as the source.
     A network administrator, if necessary, could configure the
     default router for the subnet that the WTP is on with a helper
     address and unicast it to any address on a different subnet.
 5.  IP Multicast: A WTP can send the above payload to a SLAPP IP
     multicast address [TBD].
 6.  DNS: If there is no DNS FQDN configured on the WTP, and the WTP
     is unable to discover an AC by any of the above methods, then it
     should attempt to query the DNS server for a well-known FQDN of
     an AC [TBD].  If this DNS query succeeds, then the WTP should
     address the SLAPP discover request packet to the unicast address
     of the AC.

Narasimhan, et al. Historic [Page 17] RFC 5413 SLAPP February 2010

 The above process is summarized in the sequence shown in Figure 7.
 SLAPP discovery start:
    Static IP address config option:
      Is a static IP address for an AC configured?
        If yes, send SLAPP discover request to that unicast IP address
          SLAPP discover response within discovery_timer?
            If yes, go to "done"
            If not, go to "Static FQDN config option"
        If not, go to "Static FQDN config option"
    Static FQDN config option:
      Is a static FQDN configured?
        If yes, send a DNS query for the IP address for the FQDN.
        Is DNS query successful?
          If yes, send SLAPP discover request to that IP address
          SLAPP discover response within discovery timer?
            If yes, go to "done"
            If not, go to "DHCP options option"
          If not, go to "DHCP options option"
     DHCP options option:
       Is the IP address of an AC present in the DHCP response?
         If yes, send SLAPP discover request to the AC's IP address
         SLAPP discover response within discovery timer?
           If yes, go to "done"
           If not, go to "Broadcast option"
         If not, go to "Broadcast option"
     Broadcast option:
       Send SLAPP discover packet to the broadcast address
       SLAPP discover response within discovery timer?
         If yes, go to "done"
         If not, go to "Multicast option"
     Multicast option:
       Send SLAPP discover packet to the SLAPP multicast address
       SLAPP discover response within discovery timer?
         If yes, go to "done"
         If not, go to "DNS discovery option"
     DNS discovery option:
       Query the DNS server for a well-known DNS name
       Is the DNS discovery successful?
         If yes, send SLAPP discover request to that IP address
         SLAPP discover response within discovery timer?
           If yes, go to "done"
           If not, go to "SLAPP discovery restart"
         If not, go to "SLAPP discovery restart"

Narasimhan, et al. Historic [Page 18] RFC 5413 SLAPP February 2010

     SLAPP discovery restart:
       Set timer for SLAPP discovery idle timer
       When timer expires, go to "SLAPP discovery start"
     done:
       Go to the next step
                               Figure 7

4.6.2. AC

 When an AC receives a SLAPP discover request, it must determine
 whether or not it wishes to acquire the WTP.  An AC MAY only agree to
 acquire those WTPs whose WTP Identifiers are statically configured in
 its configuration.  Or an AC that is willing to gratuitously acquire
 WTPs MAY accept any request pending authentication.  An AC MUST only
 choose to acquire WTPs that speak a common Negotiated Control
 Protocol, but other factors may influence its decision.  For
 instance, if the Negotiated Control Protocol is the Image Download
 protocol defined in this memo, the AC MUST NOT acquire a WTP for
 which it does not have a compatible image to download as determined
 by the WTP's HW Vendor ID, HW Version, and Software Version.
 Whatever its decision, the AC MUST respond one of two ways.
 1.  The AC sends a SLAPP discover response indicating its agreement
     to acquire the WTP.
 2.  The AC silently drops the SLAPP discover request and does not
     respond at all.

5. Security Association

 Once an AC has been discovered by a WTP and agreed to acquire it (by
 sending a Discover Response), it will initiate a DTLS [6] [8]
 exchange with the WTP by assuming the role of the "client".  The WTP
 assumes the role of the "server".  The port used by both the WTP and
 AC for this exchange will be [TBD].
 An obvious question is "Why is the AC acting as a client?".  The
 reason is to allow for non-mutual authentication in which the WTP is
 authenticated by the AC (see Section 5.1.2).
 Informational note: DTLS is used because it provides a secure and
 connectionless channel using a widely accepted and analyzed protocol.
 In addition, the myriad of authentication options in DTLS allows for
 a wide array of options with which to secure the channel between the
 WTP and the AC -- mutual and certificate-based; asymmetric or non-
 mutual authentication; anonymous authentication, etc.  Furthermore,
 DTLS defines its own fragmentation and reassembly techniques as well

Narasimhan, et al. Historic [Page 19] RFC 5413 SLAPP February 2010

 as ways in which peers agree on an effective MTU.  Using DTLS
 obviates the need to redefine these aspects of a protocol and
 therefore lessens code bloat as the same problem doesn't need to be
 solved yet again in another place.
 Failure of the DTLS handshake protocol will cause both parties to
 abandon the exchange.  The AC SHOULD blacklist this WTP for a period
 of time to prevent a misconfigured WTP from repeatedly discovering
 and failing authentication.  The WTP MUST return to the discovery
 state of SLAPP to locate another suitable AC with which it will
 initiate a DTLS exchange.
 Once the DTLS handshake has succeeded, the WTP and AP transition into
 "image download state" and protect all further SLAPP messages with
 the DTLS-negotiated cipher suite.

5.1. Example Authentication Models (Informative)

 Any valid cipher suite in [7] can be used to authenticate the WTP
 and/or the AC.  Different scenarios require different authentication
 models.  The following examples are illustrative only and not meant
 to be exhaustive.
 Since neither side typically involves a human being, a username/
 password-based authentication is not possible.
 Zero-config requirements on certain WTP deployments can predicate
 certain authentication options and eliminate others.

5.1.1. Mutual Authentication

 When mutually authenticating, the WTP authenticates the AC, thereby
 ensuring that the AC to which it is connecting is a trusted AC, and
 the AC authenticates the WTP, thereby ensuring that the WTP that is
 connecting is a trusted WTP.
 Mutual authentication is typically achieved by using certificates on
 the WTP and AC, which ensure public keys each party owns.  These
 certificates are digitally signed by a Certification Authority, a
 trusted third party.
 Enrolling each WTP in a Certification Authority is outside the scope
 of this document, but it should be noted that a manufacturing
 Certification Authority does not necessarily provide the level of
 assurance necessary as it will only guarantee that a WTP or AC was
 manufactured by a particular company and cannot distinguish between a
 trusted WTP and a WTP that is not trusted but was purchased from the
 same manufacturer as the AC.

Narasimhan, et al. Historic [Page 20] RFC 5413 SLAPP February 2010

5.1.2. WTP-Only Authentication

 Some deployments may only require the WTP to authenticate to the AC
 and not the other way around.
 In this case, the WTP has a keypair that can uniquely identify it
 (for example, using a certificate) and, that keypair is used in a
 "server-side authentication" [7] exchange.
 This authentication model does not authenticate the AC and a rogue AC
 could assert control of a valid WTP.  It should be noted, though,
 that this will only allow the WTP to provide service for networks
 made available by the rogue AC.  No unauthorized network access is
 possible.

5.1.3. Anonymous Authentication

 In some deployments, it MAY just be necessary to foil the casual
 snooping of packets.  In this case, an unauthenticated, but
 encrypted, connection can suffice.  Typically a Diffie-Hellman
 exchange is performed between the AC and WTP and the resulting
 unauthenticated key is used to encrypt traffic between the AC and
 WTP.

6. SLAPP Control Protocols

 In this section, we describe two extensions for SLAPP -- one that is
 specific to 802.11 WLANs and another that is a technology-neutral
 protocol by which an AC can download a bootable image to a WTP.

6.1. 802.11 Control Protocol for SLAPP

 This section describes a SLAPP extension that is targeted towards
 WTPs and ACs implementing the IEEE 802.11 WLAN standard.  This
 extension contains all the technology-specific components that will
 be used by an AC to control and manage 802.11 WTPs.

6.1.1. Supported CAPWAP Architectures

 The CAPWAP architecture taxonomy document [2] describes multiple
 architectures that are in use today in the WLAN industry.  While
 there is a wide spectrum of variability present in these documented
 architectures, supporting every single variation or choice would lead
 to a complex protocol and negotiation phase.  In the interest of
 limiting the complexity of the 802.11 component, we have limited the
 negotiation to four different architectural choices as listed below:

Narasimhan, et al. Historic [Page 21] RFC 5413 SLAPP February 2010

 Local MAC, bridged mode:  This mode of operation falls under the
    Local MAC architecture.  The 802.11 MAC is terminated at the WTP.
    The WTP implements an L2 bridge that forwards packets between its
    WLAN interface and its Ethernet interface.
 Local MAC, tunneled mode:  This mode of operation also falls under
    the Local MAC architecture where the 802.11 MAC is terminated at
    the WTP.  The difference between this mode and the previous one is
    that in this mode, the WTP tunnels 802.3 frames to the AC using
    the mechanisms defined in Section 6.1.2.
 Split MAC, L2 crypto at WTP:  This mode of operation falls under the
    Split MAC architecture.  The 802.11 MAC is split between the WTP
    and the AC, the exact nature of the split is described in Section
    6.1.1.2.  The L2 crypto functions are implemented in the WTP are
    the ones used to satisfy this function irrespective of whether or
    not the AC is also capable of this function.  The WTP tunnels L2
    frames to the AC using mechanisms defined in Section 6.1.2.
 Split MAC, L2 crypto at AC:  This mode of operation also falls under
    the Split MAC architecture.  The difference between this one and
    the previous one is that the L2 crypto functions implemented in
    the AC are used to satisfy this function irrespective of whether
    or not these functions are also available at the WTP.  The WTP
    tunnels L2 frames to the AC using mechanisms defined in Section
    6.1.2.

6.1.1.1. Local MAC

 The Local MAC architecture as documented in the CAPWAP architecture
 taxonomy document [2] performs all 802.11 frame processing at the
 WTP.  The conversion from 802.11 to 802.3 and vice versa is also
 implemented at the WTP.  This would mean that other functions like
 fragmentation/reassembly of 802.11 frames, and encryption/decryption
 of 802.11 frames is implemented at the WTP.

6.1.1.1.1. Bridged Mode

 In this sub-mode of the Local MAC architecture, the 802.11 frames are
 converted to 802.3 frames and bridged onto the Ethernet interface of
 the WTP.  These frames may be tagged with 802.1Q VLAN tags assigned
 by the AC.

Narasimhan, et al. Historic [Page 22] RFC 5413 SLAPP February 2010

6.1.1.1.2. Tunneled Mode

 In this sub-mode of the Local MAC architecture, the 802.11 frames are
 converted to 802.3 frames and are tunneled (using the tunneling
 mechanism defined in Section 6.1.2) to the AC to which the WTP is
 attached.  These frames may be tagged with 802.1Q VLAN tags assigned
 by the AC.

6.1.1.2. Split MAC

 In the Split MAC architecture, the MAC functions of an 802.11 AP are
 split between the WTP and the AC.  The exact nature of the split is
 dependent upon the sub-modes listed in this section.  In both cases,
 frames are tunneled to the AC using the mechanism defined in Section
 6.1.2.
 Some of these Split MAC architectures convert the 802.11 frames into
 802.3 frames, which may be 802.1Q-tagged using tags assigned by the
 AC, while other of these Split MAC architectures will tunnel the
 entire 802.11 frame to the AC.  The AC and WTP agree on what type of
 frame will be tunneled during the control protocol registration in
 Section 6.1.3

6.1.1.2.1. L2 Crypto at the WTP

 For this sub-mode of the Split MAC architecture, the 802.11 AP
 functions are split as follows:
 At the WTP:
    802.11 control frame processing
    802.11 encryption and decryption
    802.11 fragmentation and reassembly
    Rate Adaptation
    802.11 beacon generation
    Power-save buffering and Traffic Indication Map (TIM) processing
 At the AC:
    802.11 Management frame processing
    802.11 DS and portal

Narasimhan, et al. Historic [Page 23] RFC 5413 SLAPP February 2010

 Split MAC implementations of this kind may tunnel either 802.11 or
 802.3 frames between the AC and the WTP.

6.1.1.2.2. L2 Crypto at the AC

 For this sub-mode of the Split MAC architecture, the 802.11 AP
 functions are split as follows:
 At the WTP:
    802.11 control frame processing
    Rate Adaptation
    802.11 beacon generation
    Power-save buffering and TIM processing
 At the AC:
    802.11 Management frame processing
    802.11 encryption and decryption
    802.11 fragmentation and reassembly
    802.11 DS and portal
 Split MAC implementations of this kind tunnel 802.11 frames between
 the AC and the WTP.

6.1.2. Transport

 The 802.11 Control Protocol has two components, one for transporting
 the specific control and provisioning messages and another to tunnel
 data traffic from the WTP to the AC.
 The SLAPP 802.11 Control Protocol uses the Generic Routing
 Encapsulation (GRE) [4] to encapsulate L2 frames.  Depending on
 whether and how an architecture splits its MAC, some architectures
 may tunnel 802.11 frames directly to the AC while others may tunnel
 802.3 frames, which may be optionally 802.1Q-tagged using tags
 assigned by the AC.

Narasimhan, et al. Historic [Page 24] RFC 5413 SLAPP February 2010

 The delivery mechanism of these GRE packets is IP.  Therefore, the IP
 protocol of the outer packet is 47, indicating a GRE header follows.
 When GRE encapsulates 802.11 frames, the ether type in the GRE header
 is TBD; when GRE encapsulates 802.3 frames, the ether type in the GRE
 header is TBD2.
 Since IP is the delivery mechanism, all issues governing
 fragmentation and reassembly are handled by [5].

6.1.2.1. SLAPP 802.11 Control Protocol Header

 When using the 802.11 Control Protocol, the type of SLAPP message is
 four (4), "control protocol packet".  In this case, a two (2) octet
 field is appended to the SLAPP header to indicate the control
 protocol type as shown in Figure 8.  The SLAPP 802.11 Control
 Protocol takes place in the "Negotiated Control Protocol" phase of
 Section 4.1, and all SLAPP 802.11 Control Protocol messages are
 therefore secured by the security association created immediately
 prior to entering that phase.
     0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  802.11 Control Protocol Type |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 8: SLAPP Control Protocol Header
 Where valid 802.11 Control Protocol Types are:
    1 : Registration Request - sent from WTP to AC
    2 : Registration Response - sent from AC to WTP
    3 : De-Registration Request - sent by either WTP or AC
    4 : De-Registration Response - sent by the recipient of the
        corresponding request
    5 : Configuration Request - sent by WTP to AC
    6 : Configuration Response - sent by AC to WTP
    7 : Configuration Update - sent by AC to WTP
    8 : Configuration Acknowledgment - sent by the WTP to AC

Narasimhan, et al. Historic [Page 25] RFC 5413 SLAPP February 2010

    9 : Status Request - sent by the AC to the WTP
    10 : Status Response - sent by the WTP to the AC
    11 : Statistics Request - sent by the AC to the WTP
    12 : Statistics Response - sent by the WTP to the AC
    13 : Event - sent by the WTP to the AC
    14 : Keepalive - sent either way
    15 : Key Config Request - sent by the AC to the WTP
    16 : Key Config Response - sent by the WTP to the AC

6.1.3. Provisioning and Configuration of WTP

 All basic configuration functions are applicable per-Extended Service
 Set Identifier (ESSID) per-radio in a WTP.  Some WTPs MAY support
 more than one ESSID per-radio, while all WTPs MUST support at least
 one ESSID per-radio, which may be considered the primary ESSID in
 case of multiple ESSID support.  All per-WTP configurations and
 capabilities (e.g., number of radios) are handled as part of the
 discovery and initialization process.
 The provisioning of the regulatory domain of a WTP is beyond the
 scope of this document.  A WTP, once provisioned for a specific
 regulatory domain, MUST restrict the operational modes, channel,
 transmit power, and any other necessary limits based on the knowledge
 contained within its software image and hardware capabilities.  The
 WTP MUST communicate its capabilities limited by the regulatory
 domain as well as by the WTP hardware, if any, to the AC during the
 capability exchange.
 The allocation and assignment of Basic Service Set Identifiers
 (BSSIDs) to the primary interface and to the virtual access point
 (AP) interfaces, if supported, are outside the scope of this
 document.

6.1.3.1. Information Elements

 Information elements (IEs) are used to communicate capability,
 configuration, status, and statistics information between the AC and
 the WTP.

Narasimhan, et al. Historic [Page 26] RFC 5413 SLAPP February 2010

6.1.3.1.1. Structure of an Information Element

 The structure of an information element is show below.  The element
 ID starts with an element ID octet, followed by a 1-octet length, and
 the value of the element ID whose length is indicated in the Length
 field.  The maximum length of an element is 255 octets.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   Element ID  |     Length    |   Value ....                  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.1.3.1.2. CAPWAP Mode

 This element defines the MAC architecture modes (Section 6.1.1).
    Element ID : 1
    Length : 1
    Value : The following values are defined.
    Bit 0 : CAPWAP mode 1 - Local MAC, bridged mode
    Bit 1 : CAPWAP mode 2 - Local MAC, tunneled mode
    Bit 2 : CAPWAP mode 3 - Split MAC, WTP encryption, 802.3 tunneling
    Bit 3 : CAPWAP mode 4 - Split MAC, WTP encryption, 802.11
            tunneling
    Bit 4 : CAPWAP mode 5 - Split MAC, AC encryption, 802.11 tunneling
    Bits 5-7 : Set to 0
 When this element is included in the capabilities message, then the
 setting of a bit indicates the support for this CAPWAP mode at the
 WTP.  When this element is used in configuration and status messages,
 then exactly one of bits 0-4 MUST be set.

6.1.3.1.3. Number of WLAN Interfaces

 This element refers to the number of 802.11 WLANs present in the WTP.
    Element ID : 2
    Length : 1

Narasimhan, et al. Historic [Page 27] RFC 5413 SLAPP February 2010

    Value : 0-255

6.1.3.1.4. WLAN Interface Index

 This element is used to refer to a particular instance of a WLAN
 interface when used in configuration and status messages.  When used
 within a recursion element, the elements within the recursion element
 correspond to the WLAN interface specified in this element.
    Element ID : 3
    Length : 1
    Value : 0 - (Number of WLAN interfaces - 1)

6.1.3.1.5. WLAN Interface Hardware Vendor ID

 This element is the WLAN Interface hardware vendor's SMI enterprise
 code in network octet order (these enterprise codes can be obtained
 from, and registered with, IANA).  This field appears once for each
 instance of WLAN interface present in the WTP.
    Element ID : 4
    Length : 4
    Value : 32-bit value

6.1.3.1.6. WLAN Interface Type ID

 This element is an ID assigned by the WLAN Interface hardware vendor
 to indicate the type of the WLAN interface.  It is controlled by the
 hardware vendor and the range of possible values is beyond the scope
 of this document.  This field appears once for each instance of a
 WLAN interface present in the WTP.
    Element ID : 5
    Length : 4

6.1.3.1.7. Regulatory Domain

 If a regulatory domain is provisioned in the WTP, then the WTP
 indicates this by including this element in the capabilities list.
 If this information is not available at the WTP, then this element
 SHOULD not be included in the capabilities list.  The process by
 which this information is provisioned into the WTP is beyond the
 scope of this document.

Narasimhan, et al. Historic [Page 28] RFC 5413 SLAPP February 2010

    Element ID : 6
    Length : 4
    Value : ISO code assigned to the regulatory domain

6.1.3.1.8. 802.11 PHY Mode and Channel Information

 This element indicates the list of 802.11 Physical Layer (PHY) modes
 supported by the WTP along with a list of channels and maximum power
 level supported for this mode.  This element appears once for each
 instance of WLAN interface at the WTP.  There could be multiple
 instances of this element if the WLAN interface supports multiple PHY
 types.
    Element ID : 7
    Length : Variable
    Valid : This field consists of
    PHY mode : With a length of 1 octet with values as follows:
       0 : Radio Disabled/Inactive
       1 : IEEE 802.11b
       2 : IEEE 802.11g
       3 : IEEE 802.11a
       4-255 : Reserved
    Power Level : In the capabilities messages, this indicates the
       maximum power level supported in this mode by the WTP; while in
       the configuration and status messages, this field indicates the
       desired power level or the current power level that the WTP is
       operating at.  The field has a length of 1 octet and the power
       level is indicated in dBm.
    Channel Information : A variable number of 2-octet values that
       indicate the center frequencies (in KHz) of all supported
       channels in this PHY mode.
 When this element is used in configuration and status messages, the
 Power Level field indicates the desired or current operating power
 level.  The Channel field has exactly one 2-octet value indicating
 the desired or current operating frequency.

Narasimhan, et al. Historic [Page 29] RFC 5413 SLAPP February 2010

6.1.3.1.9. Cryptographic Capability

 In the capabilities message, this element contains the list of
 cryptographic algorithms that are supported by the WTP.  This appears
 once for each instance of the WLAN interface present in the WTP.  In
 configuration and status messages, this element is used to indicate
 the configured cryptographic capabilities at the WTP.
    Element ID : 8
    Length : 1
    Value : The following bits are defined:
       Bit 0 : WEP
       Bit 1 : TKIP
       Bit 2 : AES-CCMP
       Bits 3-7 : Reserved

6.1.3.1.10. Other IEEE 802.11 Standards Support

 This element contains a bitmap indicating support at the WTP for
 various IEEE 802.11 standards.
    Element ID : 9
    Length : 4
    Value : A bitmap as follows:
       Bit 0 : WPA
       Bit 1 : 802.11i
       Bit 2 : WMM
       Bit 3 : WMM-SA
       Bit 4 : U-APSD
       Bits 5-32 : Reserved

Narasimhan, et al. Historic [Page 30] RFC 5413 SLAPP February 2010

6.1.3.1.11. Antenna Information Element

 In the capabilities message, this element is formatted as follows
    Element ID : 10
    Length : 4
    Value : Formatted as follows:
       Bits 0-7 : Number of Antennae
       Bit 8 : Individually Configurable, 0 = No, 1 = Yes
       Bit 9 : Diversity support, 0 = No, 1 = Yes
       Bit 10 : 0 = Internal, 1 = External
       Bits 11-31 : Reserved
 In configuration and status messages, this element is formatted as
 follows:
    Element ID : 10
    Length : 4
    Value : Formatted as follows:
       Bits 0-7 : Antenna Number - is a number between 0 and the
       number of antennae indicated by the WTP.  The value is valid
       only if Bit 8 is set; otherwise, it MUST be ignored.
       Bit 8 : Antenna Select - if this bit is reset, then the antenna
       selection is left to the algorithm on the WTP.  If this bit is
       set, then the Antenna Number field indicates the antenna that
       should be used for transmit and receive.
       Bits 9-31 : Reserved

6.1.3.1.12. Number of BSSIDs

 This element indicates the number of BSSIDs supported by the WLAN
 interface.  This element is optional in the capabilities part of the
 registration request message, and if it is absent, then the number of
 BSSIDs is set to 1.  This element appears once for each instance of a
 WLAN interface present in the WTP.

Narasimhan, et al. Historic [Page 31] RFC 5413 SLAPP February 2010

    Element ID : 11
    Length : 1
    Value : The number of BSSIDs that the WLAN interface is capable of
    supporting.

6.1.3.1.13. BSSID Index

 This element is used when sending configuration or status specific to
 a certain BSSID in the WTP.
    Element ID : 12
    Length : 1
    Valid values are from 0 to (Number of BSSIDs -1)

6.1.3.1.14. ESSID

 This element is used in configuration and status messages to either
 configure the ESSID on a certain BSSID or report the current
 operating value.
    Element ID : 13
    Length : Variable, between 0 and 32 both inclusive.
    Value : Variable, contains ASCII characters.
 There is no default value for this parameter.

6.1.3.1.15. ESSID Announcement Policy

 This element is used in configuration and status messages to control
 the announcement of the ESSID in 802.11 beacons.  For the Local MAC
 modes of operation, this field is also used to control whether the
 WTP should respond to Probe Requests that have a NULL ESSID in them.
    Element ID : 14
    Length : 1
    Value : Defined as follows:
    Bit 0 : ESSID announcement, 0 = Hide ESSID, 1 = Display ESSID in
            802.11 beacons.  The default value for this bit is 1.

Narasimhan, et al. Historic [Page 32] RFC 5413 SLAPP February 2010

    Bit 1 : Probe Response policy, 0 = Respond to Probe Requests that
            contain a NULL ESSID, 1 = Respond only to Probe Requests
            that match the configured ESSID.  The default value for
            this bit is 0.
    Bit 2-7 : Reserved

6.1.3.1.16. Beacon Interval

 This element is used to configure the beacon interval on a BSSID on
 the WTP.
    Element ID : 15
    Length : 2
    Value : Valid values for the beacon interval as allowed by IEEE
    802.11
 The default value for this parameter is 100.

6.1.3.1.17. DTIM period

 This element is used to configure the DTIM period on a BSSID present
 on the WTP.
    Element ID : 16
    Length : 2
    Value : Valid values for the DTIM period as allowed by IEEE
    802.11.
 The default value for this parameter is 1.

6.1.3.1.18. Basic Rates

 Configure or report the configured set of basic rates.
    Element ID : 17
    Length : 4
    Value : Each of the bits in the following list is interpreted as
    follows.  If the bit is set, then that particular rate is to be
    configured as a basic rate.  If the bit is reset, then the rate is
    not to be configured as a basic rate.

Narasimhan, et al. Historic [Page 33] RFC 5413 SLAPP February 2010

       Bit 0 : 1 Mbps
       Bit 1 : 2 Mbps
       Bit 2 : 5.5 Mbps
       Bit 3 : 11 Mbps
       Bit 4 : 6 Mbps
       Bit 5 : 9 Mbps
       Bit 6 : 12 Mbps
       Bit 7 : 18 Mbps
       Bit 8 : 24 Mbps
       Bit 9 : 36 Mbps
       Bit 10 : 48 Mbps
       Bit 11 : 54 Mbps
       Bits 12-31 : Reserved

6.1.3.1.19. Supported Rates

 Configure or report the configured set of basic rates.
    Element ID : 18
    Length : 4
    Value : Each of the bits in the following list is interpreted as
    follows.  If the bit is set, then that particular rate is to be
    configured as a supported rate.  If the bit is reset, then the
    rate is not to be configured as a supported rate.
       Bit 0 : 1 Mbps
       Bit 1 : 2 Mbps
       Bit 2 : 5.5 Mbps
       Bit 3 : 11 Mbps
       Bit 4 : 6 Mbps

Narasimhan, et al. Historic [Page 34] RFC 5413 SLAPP February 2010

       Bit 5 : 9 Mbps
       Bit 6 : 12 Mbps
       Bit 7 : 18 Mbps
       Bit 8 : 24 Mbps
       Bit 9 : 36 Mbps
       Bit 10 : 48 Mbps
       Bit 11 : 54 Mbps
       Bits 12-31 : Reserved

6.1.3.1.20. 802.11 Retry Count

 This element is used to configure long and short retries for each
 BSSID present on the WTP.
    Element ID : 19
    Length : 2
    Value : as follows:
       Bits 0-7 : Short retry count, default value is 3.
       Bits 8-15 : Long retry count, default value is 3.

6.1.3.1.21. Fragmentation Threshold

 This element is used to configure the fragmentation threshold on a
 BSSID present on the WTP.
    Element ID : 20
    Length : 2
    Value : Valid values for the fragmentation threshold as allowed by
    IEEE 802.11.
 The default value for this parameter is 2346.

Narasimhan, et al. Historic [Page 35] RFC 5413 SLAPP February 2010

6.1.3.1.22. RTS Threshold

 This element is used to configure the Request to Send (RTS) threshold
 on a BSSID present on the WTP.
    Element ID : 21
    Length : 2
    Value : Valid values for RTS threshold as allowed by IEEE 802.11.
 The default value for this parameter is 2346.

6.1.3.1.23. Short/Long Preamble

 This element is used to configure the preamble type used for
 transmission in 802.11b mode.
    Element ID : 22
    Length : 1
    Value : Defined as follows:
       0 : Disable Short preamble
       1 : Enable Short preamble
       2-255 : Reserved
 The default value for this parameter is 0.

6.1.3.1.24. 802.1Q Tag

 This element is used to configure the tagging of packets belonging to
 a particular SSID when transferred between the AC and the WTP in
 CAPWAP modes 2-3, or before the WTP bridges the 802.3 frame to its
 wired interface when operating in CAPWAP mode 1.
    Element ID : 23
    Length : 2
    Value : 802.1Q tag
 If this element is absent in the configuration, then the WTP MUST
 assume that no tagging is required and should expect to receive
 untagged frames on frames destined towards the wireless interface.

Narasimhan, et al. Historic [Page 36] RFC 5413 SLAPP February 2010

6.1.3.1.25. SLAPP Registration ID

 A successful registration response from an AC to a WTP MUST contain
 this element.  It is used in messages between the WTP and the AC on
 all other messages during the duration for which the registration is
 active.
    Element ID : 24
    Length : 4
    Value : A 32-bit unsigned number allocated by the AC

6.1.3.1.26. WTP Name

 The AC uses this element to assign a string of ASCII characters to
 the WTP.
    Element ID : 25
    Length : Variable, between 0 and 64 both inclusive
    Value : A variable length string of ASCII characters

6.1.3.1.27. Event Filter

 The AC uses this element to assign importance to events, enable or
 disable notification, and to configure the global event notification
 policy.  When the Event Identifier is 0, this element serves as a
 global notification policy message.  The bitmap indicates the types
 of events that require the WTP to generate a notification.  When the
 Event Identifier is non-zero, this element is used to configure a
 specific event for notification and its importance level.  The
 importance level is specified by setting exactly one bit in the
 bitmap.  If none of the bits are set in the bitmap, the element
 should be interpreted as a cancellation request.  The WTP should stop
 sending notifications for the corresponding event specified in the
 Element Identifier.
    Element ID : 26
    Length : 4
    Value : Defined as follows:
       Bits 0 - 15: Event Identifier
       Bit 16: Fatal - The system is not usable.

Narasimhan, et al. Historic [Page 37] RFC 5413 SLAPP February 2010

       Bit 17: Alert - Immediate action is required.
       Bit 18: Critical
       Bit 19: Error
       Bit 20: Warning
       Bit 21: Notification
       Bit 22: Informational
       Bit 23: Debug
       Bits 24 - 31: Reserved

6.1.3.1.28. Radio Mode

 The AC uses this element to indicate the mode of operation for the
 radio for each WLAN interface.
    Element ID : 27
    Length : 1
    Value : The following are valid values:
       0 : Radio is disabled
       1 : Radio is enabled
       2-255 : Reserved

6.1.3.1.29. IEEE 802.11e Element

 The AC uses this element to configure 802.11e functions at the WTP.
    Element ID : 28
    Length : 4
    Value : A bitmap as follows:
       Bit 0 : WMM
       Bit 1 : WMM-SA
       Bit 2 : U-APSD

Narasimhan, et al. Historic [Page 38] RFC 5413 SLAPP February 2010

       Bits 3-32 : Reserved

6.1.3.1.30. Configuration Statistics

 This element defines the statistics relating to configuration and
 registration events as seen by the WTP.
    Element ID : 29
    Length : 32
    Value : The value is as follows:
  • Configuration Requests : 4 octets - Number of Configuration

Request messages sent by the WTP since the last reboot or reset

       of the counters.
  • Configuration Responses : 4 octets
  • Configuration Updates : 4 octets
  • Configuration ACKs : 4 octets
  • Registration Requests : 4 octets
  • Registration Responses : 4 octets
  • De-Registration Requests : 4 octets
  • De-Registration Responses : 4 octets

6.1.3.1.31. Transmit Frame Counters

 This information element contains a set of counters relating to the
 transmit side of the wireless link at the WTP.  These counters apply
 to either a BSS or an Access Category (if Wireless Multimedia (WMM)
 is enabled).
    Element ID : 30
    Length : 112 octets
    Value : The value of this element is defined as follows:
  • Total received from the network : 4 octets
  • Successfully transmitted frames (total) : 4 octets

Narasimhan, et al. Historic [Page 39] RFC 5413 SLAPP February 2010

  • Successfully transmitted 802.11 Mgmt frames : 4 octets
  • Successfully transmitted 802.11 Data frames : 4 octets
  • Transmitted 802.11 Control frames : 4 octets
  • Frames that reached max-retry limit : 4 octets
  • Transmitted frames with 1 retry attempt : 4 octets
  • Transmitted frames with 2 retry attempts : 4 octets
  • Transmitted frames with more than 2 retry attempts : 4 octets
  • Frames transmitted at each 802.11 PHY rate : 12*4 octets - The

counters indicate the number of frames at each of the following

       rates, respectively: 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48,
       54 Mbps.
  • Total frame dropped : 4 octets
  • Frames dropped due to insufficient resources : 4 octets
  • Frames dropped due to power-save timeouts : 4 octets
  • Frames dropped due to other reasons : 4 octets
  • Fragments transmitted : 4 octets
  • Fragments dropped : 4 octets
  • Power-save multicast frames : 4 octets
  • Power-save unicast frames : 4 octets

6.1.3.1.32. Received Frame Counters

 This information element includes all statistics related to the
 reception of the frames by WTP.  These counters apply to either a BSS
 or an Access Category (if WMM is enabled).
    Element ID : 31
    Length : 108 octets
    Value : The value of this element is defined as follows:
  • Total Frames received : 4 octets

Narasimhan, et al. Historic [Page 40] RFC 5413 SLAPP February 2010

  • Frames with the retry bit set : 4 octets
  • 802.11 Data frames received : 4 octets
  • 802.11 Mgmt frames received : 4 octets
  • 802.11 Control frames received : 4 octets
  • Cyclic Redundancy Check (CRC) errors : 4 octets
  • PHY errors : 4 octets
  • Total Fragments received : 4 octets
  • Reassembled frames : 4 octets
  • Reassembly failures : 4 octets
  • Successful Decryption : 4 octets
  • Decryption failures : 4 octets
  • Rate statistics : 48 octets - The number of frames received at

each of the 802.11 PHY rates, respectively - 1, 2, 5.5, 11, 6,

       9, 12, 18, 24, 36, 49, 54 Mbps.
  • Total frames dropped : 4 octets
  • Frames dropped due to insufficient resources : 4 octets
  • Frames dropped due to other reasons : 4 octets

6.1.3.1.33. Association Statistics

 This element includes information about the current stations
 associated with the BSS.
    Element ID : 32
    Length : Variable
    Value : The value is defined as follows:
  • Total association requests : 4 octets
  • Total associations accepted : 4 octets
  • Total associations rejected : 4 octets

Narasimhan, et al. Historic [Page 41] RFC 5413 SLAPP February 2010

  • Current associations : 4 octets
  • For each associated station,
       +  Station MAC address : 6 octets
       +  Power save state : 1 octet
       +  Current Tx rate : 1 octet
       +  Rate of last packet : 1 octet
       +  Preamble type : 1 octet
       +  WMM/U-APSD state : 1 octet

6.1.3.1.34. Status Element

 The status IE is included in the status response message sent by the
 WTP to the AC.  It contains a set of fields that are used to indicate
 the status of various states at the WTP or each BSS configured in the
 WTP.
    Element ID : 33
    Length : 2 octets
    Value : The value is defined as follows:
       Enterprise Resource Planning (ERP) element, if applicable.  If
       not applicable, then this field MUST be set to 0.
       Noise Floor : 1 octet

6.1.3.1.35. Event Configuration

 This element is used by the AC to configure the set of events that it
 wants to be notified by the WTP.
    Element ID : 34
    Length : 4 octets
    Value : The value is defined as follows:
  • Radar Detection - 1 octet

Narasimhan, et al. Historic [Page 42] RFC 5413 SLAPP February 2010

       +  Bit 0 : 1 = notify on detecting radar interference, 0
          otherwise.
       +  Bit 1 : 1 = notify of channel change due to radar
          interference, 0 otherwise.
       +  All other bits are reserved.
  • Excessive Retry Event - 1 octet. Number of successive frames

that have not been acknowledged by a client. A value of 0

       disables notification.
  • Noise Floor Threshold - 1 octet. Defines the threshold above

which an event would be generated by the WTP.

  • 802.11 Management and Action Frame Notification - 1 octet.
       +  Bit 0 : If set, notify the AC of Probe Requests from
          stations (please use with caution).  If reset, then no Probe
          Response notification is needed.
       +  Bit 1 : If set, the WTP should notify the AC of all other
          management frames from stations.
       +  All other bits are reserved.

6.1.3.1.36. Radar Detection Event

 This element is used by the WTP to notify the AC of the detection of
 radar interference and any channel changes as a result of this
 detection.
    Element ID : 35
    Length : 10 octets
    Value : Defined as follows:
       BSSID : 6 octets.  The BSSID of the WLAN interface that
       detected the radar interference.
       Channel : 2 octets.  The channel on which radar interference
       was detected.
       New Channel : 2 octets.  The new channel to which the WTP moved
       as a result of the detection of radar interference.

Narasimhan, et al. Historic [Page 43] RFC 5413 SLAPP February 2010

6.1.3.1.37. Excessive Retry Event

 This element is used by the WTP to indicate excessive retry events on
 transmission to an associated station.
    Element ID : 36
    Length : 14 octets
    Value : Defined as follows:
       Station MAC : 6 octets
       Associated BSSID : 6 octets
       Length of last burst of excessive retries : 2 octets.

6.1.3.1.38. Noise Floor Event

 This element is used by the WTP to notify the AC of the current noise
 floor at one of the WLAN interfaces exceeding the configured noise
 floor threshold.
    Element ID : 37
    Length : 10 octets
    Value : Defined as follows:
       BSSID : 6 octets
       Current Channel : 2 octets
       Current Noise Floor : 2 octets

6.1.3.1.39. Raw 802.11 Frame

 This element provides a generic capability for either a WTP or an AC
 to send a raw 802.11 frame to the other party.  For example, it can
 be used to notify the AC of station association/disassociation events
 in the case of Local MAC architectures.
    Element ID : 252
    Length : Variable
    Value : A raw 802.11 frame

Narasimhan, et al. Historic [Page 44] RFC 5413 SLAPP February 2010

6.1.3.1.40. Vendor-Specific Element

 This element is used to transfer vendor-specific information between
 the WTP and the AC.
    Element ID : 253
    Length : Variable, > 3
    Value : This variable-length element starts with a 3-octet
    Organizationally Unique Identifier (OUI), followed by a series of
    octets that are specific to the vendor represented by the OUI.

6.1.3.1.41. Recursion Element

 This element type can be used to recursively define a variable-length
 element that should be interpreted as a series of other elements
 defined in this section.  It can be used to bound a set of elements
 as a unit.
    Element ID : 254
    Length : Variable
    Value : A variable length element that contains a set of one or
    more elements defined in this section.

6.1.3.1.42. Pad Element

 This is a generic element type that can be used to pad the packets,
 if necessary.
    Element ID : 255
    Length : Variable
    Value : A variable-length element that MUST be filled with all 0s
    at the source and MUST be ignored at the destination.

Narasimhan, et al. Historic [Page 45] RFC 5413 SLAPP February 2010

6.1.3.2. SLAPP 802.11 Control Protocol Messages

6.1.3.2.1. Registration Request

 At the start of the SLAPP 802.11 Control Protocol, the WTP sends a
 registration request to the AC that it authenticated with.  The
 registration request carries a list of information elements
 indicating the WTP's capabilities to the AC.  The message starts with
 the SLAPP 802.11 Control Protocol header (Figure 8) with a SLAPP
 Control Protocol message type of 1.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               1               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Transaction ID                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                    Information Elements                       ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 9: SLAPP 802.11 Registration Request
    Flags : Reserved
    Transaction ID : A 32-bit random number chosen by the WTP at the
    start of a new registration phase.  This number is used in the
    registration response by the AC to match the response to the
    corresponding request.
 The following information elements are mandatory in the capabilities
 exchange:
    1 : CAPWAP mode
    2 : Number of WLAN interfaces
    For each WLAN interface:
       7 : 802.11 PHY mode and Channel Information
       8 : Cryptographic Capability
       9 : Other 802.11 standards support

Narasimhan, et al. Historic [Page 46] RFC 5413 SLAPP February 2010

 The following information elements may be optionally included in the
 registration request:
    For each WLAN interface:
       4 : WLAN Interface HW Vendor ID
       5 : WLAN Interface Type ID
       6 : Regulatory Domain
       10 : Antenna Information Element
       11 : Number of BSSIDs
       253 : Vendor-Specific Element

6.1.3.2.2. Registration Response

 Upon receiving a registration request, the AC may either chose to
 accept the WTP or reject its registration request.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               2               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Transaction ID                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                    Information Elements                       ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 10: SLAPP 802.11 Registration Response
    Flags :
       Bit 0 : Indicates the status of the transaction, 0 = successful
       response from the AC, 1 = the registration request is being
       rejected by the AC.
       Bits 1-7 : Reserved
       Bits 8-15 : If bit 0 = 1 (i.e., the registration request is
       being rejected by the AC), then this field contains a reason
       code.  Otherwise, these bits are currently set to 0.  The
       following reason codes are currently defined:

Narasimhan, et al. Historic [Page 47] RFC 5413 SLAPP February 2010

          0 : Reserved
          1 : Unspecified reason
          2 : Unable to handle more WTPs
          3 : Incompatible capabilities
          4-255 : Reserved
    Transaction ID : A 32-bit random number chosen by the WTP at the
    start of a new registration phase.  This number is used in the
    registration response by the AC to match the response to the
    corresponding request.
 The following information elements are mandatory if the transaction
 is successful:
    1 : CAPWAP mode - the mode that the AC chooses from among the list
    of supported modes sent by the WTP in the registration request.
    24 : SLAPP registration ID

6.1.3.2.3. De-Registration Request

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               3               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Reason Code                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 11: SLAPP 802.11 De-Registration Request
    Flags : Reserved
    SLAPP Registration ID : The registration ID assigned by the AC
    upon successful registration.
    Reason Code : The following are valid values:
       0 : Unspecified reason

Narasimhan, et al. Historic [Page 48] RFC 5413 SLAPP February 2010

       1 : The device that is the source of the frame is going down.
       All other values are reserved.

6.1.3.2.4. De-Registration Response

 The De-Registration Response is a simple ACK from the recipient of
 the corresponding De-Registration Request.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               4               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Reason Code                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           Figure 12: SLAPP 802.11 De-Registration Response
    Flags : Reserved
    SLAPP Registration ID : The registration ID assigned by the AC
    upon successful registration.
    Reason Code : The same reason code used in the corresponding
    request.

Narasimhan, et al. Historic [Page 49] RFC 5413 SLAPP February 2010

6.1.3.2.5. Configuration Request

 The Configuration Request message is used by the WTP to request a set
 of configurations for each BSS that the AC wishes to configure at the
 WTP.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               5               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                 Information Element ID list                   ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 13: SLAPP 802.11 Configuration Request
 The Information Element ID list field contains the list of IEs that
 the WTP is interested in obtaining configuration information for.

6.1.3.2.6. Configuration Response

 The Configuration Response message is used by the AC to respond to a
 Configuration Request by the WTP.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               6               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                 Information Element list                      ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 14: SLAPP 802.11 Configuration Response
 The following information elements are mandatory in the Configuration
 Response:
    01: CAPWAP mode
    For each WLAN interface:

Narasimhan, et al. Historic [Page 50] RFC 5413 SLAPP February 2010

       03: WLAN Interface Index
       27: Radio Mode
       07: 802.11 PHY mode and Channel Selection
       For each BSSID:
          12: BSSID Index
          13: ESSID
          08: Cryptographic Selection
 The following information elements may be optionally included in the
 Configuration Response:
    10: Antenna Information Element
    25: WTP Name
    For each WLAN interface:
       For each BSSID:
          14: ESSID Announcement Policy
          15: Beacon Interval
          16: DTIM Period
          17: Basic Rates
          18: Supported Rates
          19: Retry Count
          20: Fragmentation Threshold
          21: RTS Threshold
          22: Short/Long Preamble
          23: 802.1Q Tag
          253: Vendor-Specific Element

Narasimhan, et al. Historic [Page 51] RFC 5413 SLAPP February 2010

 If any of the optional IEs is absent in the Configuration Response
 message, then their default values are applied by the WTP.

6.1.3.2.7. Configuration Update

 The Configuration Update message is initiated by the AC to push
 modified or updated configuration to the WTP.  It has a format
 similar to that of the Configuration Response message defined above.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               7               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                 Information Element list                      ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 15: SLAPP 802.11 Configuration Update
 The list of mandatory and optional IEs for the Configuration Update
 message is the same as that for the Configuration Response message.

6.1.3.2.8. Configuration Acknowledgment

 The Configuration Acknowledgment message is used by the WTP to inform
 the AC whether it has accepted the prior Configuration Update or
 Configuration Response message.  The WTP can reject the configuration
 sent by the AC, in which case it MUST return to the discovery state.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               8               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Status Code                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 16: SLAPP 802.11 Configuration ACK
 The Status Code field contains one of the following values:

Narasimhan, et al. Historic [Page 52] RFC 5413 SLAPP February 2010

    0 : Success - The WTP accepts that the configuration pushed by the
    AC and has applied it.
    1 : Failure - The WTP did not accept the configuration pushed by
    the AC and MUST be de-registered at the AC.

6.1.3.2.9. Status Request

 The status request message is used by the AC to request the
 configuration and operational status from the WTP.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               9               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                  Information Element ID list                  ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 17: SLAPP 802.11 Status Request
 The Information Element ID list contains the list of IEs for which
 the AC requests status.

6.1.3.2.10. Status Response

 The status response message is used by the WTP to respond to a status
 request from the AC.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              10               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                   Information Element list                    ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 18: SLAPP 802.11 Status Response
 The Flags field contains one of the following values:

Narasimhan, et al. Historic [Page 53] RFC 5413 SLAPP February 2010

    Bit 0 : If set, Unknown AC or SLAPP registration ID.  If this bit
    is reset, then this indicates a successful response.
    Bit 1 : If set, the WTP indicates that it has not been configured
    yet; otherwise, the WTP is in a configured state.
    All other values are reserved.
 The status IE is mandatory in a status response message.

6.1.3.2.11. Statistics Request

 The Statistics request message is used by the AC to request
 statistics information from the WTP.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              11               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                   Information Element list                    ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 19: SLAPP 802.11 Statistics Request
 The Flags field contains the following bits:
    Bit 0 : If set to 1, then the WTP should reset the counters after
    sending the statistics response message.
    All other bits are reserved and MUST be set to 0 by the source and
    ignored by the destination.

Narasimhan, et al. Historic [Page 54] RFC 5413 SLAPP February 2010

6.1.3.2.12. Statistics Response

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              12               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                   Information Element list                    ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 20: SLAPP 802.11 Statistics Response
 The Flags field contains the following bits:
    Bit 0 : If set, then the counters have been reset as requested by
    the AC.
    Bit 1 : If set, then the WTP has encountered a statistics request
    from either an unknown AC or with an unknown SLAPP registration
    ID.
    Bit 2 : If set, WTP indicates that it has not been configured yet;
    otherwise, the WTP is in a configured state.
    All other bits are reserved.

6.1.3.2.13. Keepalive

 The keepalive messages can be initiated by either the WTP or the AC.
 It is used to probe the availability of the other party and the path
 between them.  The initial message is termed the keepalive request,
 while the response to that message is termed the keepalive response.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              13               |            Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 21: SLAPP Keepalive Packet

Narasimhan, et al. Historic [Page 55] RFC 5413 SLAPP February 2010

 The Flags field has the following values:
    Bit 0 : Set to 0 in a keepalive request message, set to 1 in a
    keepalive response message.
    Bit 1 : Set to 0 in a keepalive request message, set to 1 in a
    keepalive response message if the initiator of the keepalive
    request is unknown or the SLAPP registration ID is incorrect, and
    set to 0 otherwise.
    All other bits are reserved and must be set to 0 by the source and
    ignored at the destination.

6.1.3.2.14. Key Configuration

 In CAPWAP mode 5, the 802.11 crypto functions are performed at the
 AC.  So there is no need for the AC to send PTKs/GTKs to the WTP.
 When one of the CAPWAP Modes 1-4 has been negotiated between the AC
 and WTP, it is necessary for the AC to send both unicast and
 broadcast/multicast keys to the WTP.  This is accomplished after the
 802.1x authenticator (which resides on the AC) has successfully
 authenticated the supplicant.  Key Configuration Requests are
 differentiated -- unicast or broadcast -- by setting or clearing the
 high-order bit of the "Flags" field.  The setting of this bit
 determines the contents of the Key Configuration Request following
 the SLAPP Registration ID.

Narasimhan, et al. Historic [Page 56] RFC 5413 SLAPP February 2010

6.1.3.2.14.1. Unicast Key Configuration Request

 The Unicast Key Configuration Request is used by the AC to inform the
 WTP of the key to use when protecting unicast frames to and from a
 specified supplicant.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              15               |0|          Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     supplicant MAC address                    ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | supplicant mac address (cont) |  Supp 802.1Q tag      | RSVD  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     unicast key length        |         unicast key           ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 22: Unicast Key Configuration Request
 Note the high-order bit of the "Flags" field is cleared to indicate a
 unicast key is being sent.  The 802.1Q tag field is used to indicate
 to the WTP which VLAN this supplicant is in and which broadcast/
 multicast key to use when communicating to it with broadcast/
 multicast frames.

6.1.3.2.14.2. Broadcast/Multicast Key Configuration Request

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              15               |1|          Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    801.1q tag         | RSVD  | broadcast/multicast key length|
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                  broadcast/multicast key                      ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 23: Group Key Configuration Request

Narasimhan, et al. Historic [Page 57] RFC 5413 SLAPP February 2010

 Note the high-order bit of the "Flags" field is set, indicating a
 broadcast/multicast key is being sent.  The bits marked "RSVD" are
 reserved and MUST be set to zero by the AC and ignored by the WTP.

6.1.3.2.14.3. Unicast Key Configuration Response

 The WTP acknowledges receipt of a Unicast Key Configuration Request
 by sending a Unicast Key Configuration Response.  This response
 mirrors the request but does not send back the key length or the key
 itself.  (The RSVD bits are returned for alignment purposes and MUST
 be set to zero by the WTP and ignored by the AC.)
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              16               |0|          Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     supplicant MAC address                    ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | supplicant mac address (cont) |  Supp 802.1Q tag      | RSVD  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 24: Unicast Key Configuration Response

Narasimhan, et al. Historic [Page 58] RFC 5413 SLAPP February 2010

6.1.3.2.14.4. Multicast Key Configuration Response

 The WTP acknowledges receipt of a Multicast Key Configuration Request
 by sending a Multicast Key Configuration Response.  This response
 mirrors the request, but it does not send back the key length or the
 key itself.  (The RSVD bits are returned for alignment purposes and
 MUST be set to zero by the WTP and ignored by the AC.)
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |      4        |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |              16               |0|          Flags              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    SLAPP Registration ID                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    801.1q tag         | RSVD  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 25: Group Key Configuration Response

6.1.3.3. Monitoring and Statistics

 An AC may want to periodically monitor the health of a WTP, collect
 the necessary information for diagnostics, and get notifications on
 pre-defined events at the WTP that may be of interest.  This section
 defines a set of WTP statistics and events and describes the process
 of collecting statistics from WTPs and configuring the event
 notification mechanism at the WTP.  It is beyond the scope of this
 document to describe what should/could be done with the collected
 information.

6.1.3.3.1. Statistics Collection Procedure

 The simple statistics collection procedure defined here does not
 require the WTP to maintain any timers or any similar mechanisms.  A
 WTP is responsible only for maintaining the statistics defined in
 Information Elements 29, 30, 31, and 32.  The WTP must also respond
 to a statistics request message from the AC by delivering the
 appropriate statistics to the AC using a statistics response message.
 For example, if an AC is interested in gathering periodic statistics
 about some specific statistics, it is the responsibility of the AC to
 poll the WTP at the appropriate intervals.

Narasimhan, et al. Historic [Page 59] RFC 5413 SLAPP February 2010

6.1.3.3.2. Events Procedure

 The event notification process includes the following: 1) Event
 Registration: the registration of events of interest at the WTP by
 the AC and 2) Notification: The communication of event-related
 information by the WTP to the AC whenever the conditions for a
 specific registered event has occurred.  The set of events supported
 by a WTP and the event-specific parameters that may be configured as
 part of a event registration are given in Section 6.1.3.3.3.

6.1.3.3.3. WTP Events

 This section defines a set of WTP events along with the event-
 specific parameters that may be configured by ACs and the event-
 related information that should be delivered to the ACs by WTPs when
 the conditions for a particular configured event have occurred.
    Radar Detection Event: Configure whether the AC is interested in
    receiving a notification whenever a radar event is detected.  The
    WTP may notify the AC about the type of radar interference and the
    new channel that the WTP has moved to as a result, if any, using
    the Radar Detection Event Element (element ID: 35).
    Excessive Retry Event: Configure the number of consecutive
    transmission failures before a notification is generated.  The WTP
    may notify the MAC address of the station (STA) and the number of
    consecutive unacknowledged frames so far using the Excessive Retry
    Event Element (element ID : 36).
    Noise Floor Event: Configure the noise floor threshold above which
    an event notification would be generated by the WTP.  The WTP may
    notify the AC with the most recent measured noise floor that
    exceeded the configured threshold using the Noise Floor Event
    Element (element ID : 37).
    De-Authentication Event: Configure whether the AC is interested in
    receiving a notification whenever a station has been de-
    authenticated by the WTP.  The WTP may notify the AC with the MAC
    address of the STA along with a reason code (inactivity, etc.).
    Association Event: Needed in Local MAC architecture.
    Disassociation Event: Needed in Local MAC architecture.

6.1.4. Protocol Operation

 The SLAPP 802.11 Control Protocol operation is described in this
 section.

Narasimhan, et al. Historic [Page 60] RFC 5413 SLAPP February 2010

6.1.4.1. SLAPP 802.11 Control Protocol State Machine

6.1.4.1.1. At the WTP

     +-------------+
     | discovering |<-------------------------------+<----+
     +-------------+                                |     |
       ^  ^                                         |     |
       |  |          +-----------+                  |     |
       |  |          | securing  |                  |     |
       |  |          +----+------+                  |     |
       |  |               |                         |     |
       |  |               v                         |     |
       |  |        +--------------+                 |     |
       |  |   +--->| Unregistered |                 |     |
       |  |   |    +------+-------+                 |     |
       |  |   |           |                         |     |
       |  |   |           |Registration             |     |
       |  |   |Timeout    |Request                  |     |
       |  |   |           |                         |     |
       |  |   |           v                         |     |
       |  |   |    +--------------+                 |     |
       |  |   +----+ Registration |                 |     |
       |  |        |              |                 |     |
       |  | Reject |              |                 |     |
       |  +--------+   Pending    |                 |     |
       | nTimeout>3|              |                 |     |
       |           |              |                 |     |
       |           +------+-------+                 |     |
       |                  |                         |     |
       |                  |Accept                   |     |
       |                  |                         |     |
       |                  |                         |     |
       |                  v                         |     |
       |           +------+-------+                 |     |
       |           |  Registered  |                 |     |
       |      +--->|              |                 |     |
       |      |    +------+-------+                 |     |
       |      |           |                         |     |
       |      |Timeout    |Config                   |     |
       |      |           |Request                  |     |
       |      |           |                         |     |
       |      |           v                         |     |
       |      |    +------+-------+                 |     |
       |      +----+              |           Reject|     |
       |           |Configuration |                 |     |
       |   Reject  | Pending      |                 |     |
       +-----------+              |                 |     |

Narasimhan, et al. Historic [Page 61] RFC 5413 SLAPP February 2010

       ^ nTimeout>3+------+-------+                 |     |
       |                  |                         |     |
       |                  |                         |     |
 De-reg|                  |    +----------------+   |     |
  resp |                  |    v     Accept     |   |     |
  +----+---+       +------+----+--+           +-+---+--+  |
  |        | De-reg|              |           | Update |  |
  |  De    +<------+ Configured   +-----------+        |  |
  |Register| req   |              |           | Pending|  |
  |        |       |              |           +----+---+  |
  +--------+       +------+-------+                       |
                          |                               |
                          |                               |
                          |                               |
                      Too |Many                           |
                      Keepalive                           |
                      Failures                            |
                          |                               |
                          |                               |
                          |   De-Register                 |
                          +-------------------------------+
 In Configured and/or Registered states, respond to
 Status Requests, Statistics Requests, Keepalives, Key Config
          Figure 26: SLAPP 802.11 Control Protocol at the WTP

6.1.4.1.1.1. State Machine Explanation

 Unregistered: The transition into this state is from the securing
    state (Figure 3).  Send registration request message to move to
    Registration Pending state, set timer for registration response.
 Registration Pending: On a registration response from the AC, cancel
    registration timer.  If the response is successful, move to
    Registered state.  If not, move to discovering state (Figure 3).
    If timer expires, if nTimeout >3, then move to discovering state.
    If not, return to Unregistered state.
 Registered: Send Configuration Request message to AC to move to
    Configuration Pending state, and set timer for Configuration
    Response.  In this state, respond to status request, statistics
    request, and keepalive messages from the AC.
 Configuration Pending: If a Configuration Response is received from
    the AC, cancel the Configuration Response timer.  If the response
    is successful and the configuration is acceptable, then send the
    Configuration ACK message to AC, and move to Configured state.  If

Narasimhan, et al. Historic [Page 62] RFC 5413 SLAPP February 2010

    the Configuration Request is rejected or the configuration is not
    acceptable, then send a de-register request to the AC and move to
    discovering.  If the Configuration Response timer expires, move to
    Registered state unless nTimeout >3, in which case move to
    discovering state.
 Configured: In the Configured state, the WTP responds to the status
    request, statistics request, and keepalive messages from the AC.
    If it receives a de-register request message from the AC, then it
    sends a de-register response to the AC and moves to the
    discovering state.  If the WTP receives a Configuration Update
    message, then it moves to the Update Pending state.  If it
    receives too many consecutive keepalive failures (no responses
    from the AC to keepalive requests), then it sends a de-register
    message to the AC and moves to the discovering state.
 Update Pending: In the Update Pending state, the WTP analyzes the
    configuration information received in the Configuration Update
    message.  If the configuration is found to be acceptable, then it
    applies the configuration and returns to the Configured state.  If
    the WTP chooses to reject the configuration update, then it sends
    a de-register request to the AC and moves to the discovering
    state.
 De-register: From the Configured state, the WTP moves to the
    De-register state when it receives a de-register request message
    from the AC.  It sends a de-register response to the AC and moves
    to the discovering state.

Narasimhan, et al. Historic [Page 63] RFC 5413 SLAPP February 2010

6.1.4.1.2. At the AC

          +----------+
          | securing |
          +----+-----+
               |
               |
               |
               v
          +--------------+
 +--------| Unregistered |
 |        +----+---------+
 |             |
 |Timeout      |Register
 |             |request
 |             v                   +-------------+
 |         +----------+   Accept   | Registration|
 |     +---+Register  +----------->|  Pending    |
 |     |   |Processing|            +-+-----+-----+
 |     |   +----------+              |     |
 |     |                             |     |
 |     |Reject                    Timeout  |
 |     |                             |     |Config
 |     |                             |     |Request
 |     |      +--------------+       |     |
 |     +----->|              |<------+     |
 |            |  discovering |             v
 +----------->|              |        +------------+
              +--------------+        | Registered |
                  ^     ^  ^          +----+-------+
                  |     |  |               |
                  |     |  |               |Config
                  |     |  |               |Response
                  |     |  |               v
                  |     |  | Timeout  +------------+
                  |     |  +----------| Config     |
                  |     |   or Reject | Pending    |
                  |     |             +----+-------+
                  |     |                  |
                  |     |                  |Config ACK
                  |     |                  v
                  |     |De-Register  +------------+
                  |     +-------------|            |
                  |     or Keepalive  | Configured |<--+
                  |        failures   |            |   |
                  |                   +----+-------+   |

Narasimhan, et al. Historic [Page 64] RFC 5413 SLAPP February 2010

            Reject|                        |           |
                or|                        |           |
            Timeout     +-----------+      |Config     |
                  |     | Update    |      |Update     |
                  +-----| Pending   |<-----+           |
                        +----+------+                  |
                             |           Accept        |
                             +-------------------------+
          Figure 27: SLAPP 802.11 Control Protocol at the AC

6.1.4.1.2.1. State Machine Explanation

 The states "securing" and "discovering" are described in Figure 3.
 Unregistered: This state is entered from the securing state described
    in Figure 3.  In this state, the AC is waiting for a registration
    request message from the WTP.  Upon receiving the registration
    request message, it moves into the Registration Processing state.
 Registration Processing: In this state, the AC must determine whether
    or not it can accept the new WTP.  If the AC decides to accept the
    WTP, it must pick a CAPWAP mode to operate in and send a
    registration response message with a success code and moves to the
    Registration Pending state.  If the AC chooses to reject the
    current registration request from the WTP, it must send a
    registration response with a failure code and move to the
    discovering state.
 Registration Pending: If the timer expires before a response from the
    WTP is received, then the AC destroys the registration state and
    moves to the discovering state.  If a Configuration Request
    message is received from the WTP, then the AC moves into the
    Registered state and processes the Configuration Request message.
    It sends a Configuration Response message to the WTP with the
    appropriate IEs and moves into the Configuration Pending state.
 Configuration Pending: If the timer expires before a response is
    received from the WTP, then the AC destroys the current
    registration and moves into the discovering state.  If a
    Configuration ACK is received from the WTP, but contains a failure
    code, then the AC again destroys the registration state and moves
    into the discovering state.  If the Configuration ACK from the WTP
    is successful, then the AC moves to the Configured state.
 Configured: In the Configured state, the AC can send a status
    request, statistics request, keepalive, and Key Configuration
    messages to the WTP.  Any response to these messages from the WTP

Narasimhan, et al. Historic [Page 65] RFC 5413 SLAPP February 2010

    that indicates an unknown SLAPP registration ID or an unknown AC
    causes the AC to destroy any registration or configuration state
    and move to the discovering state.  From the configured state, the
    AC can send a Configuration Update message and move into the
    Update Pending state.  If it receives a de-register request from
    the WTP, then it destroys all current registration and
    configuration state and moves into the discovering state.  If a
    number of successive keepalive messages go unacknowledged by the
    WTP, then the AC moves into the discovering state.
 Update Pending: When the AC receives a Configuration ACK message with
    a success code, then it returns to the Configured state.  If the
    status code is a failure or if the timer expires before the
    Configuration ACK is received from the WTP, the AC destroys all
    registration and configuration state for the WTP and moves into
    the discovering state.

6.2. Image Download Protocol

 The Image Download protocol is a control protocol defined in this
 document that is generic enough to be agnostic to the underlying
 technology.
 In the Image Download protocol, the WTP obtains a bootable image from
 the AC by receiving a series of image transfer packets.  Missed image
 data packets are re-requested by the WTP by sending image data
 request packets indicating the missing packets.
 The image to download is divided into slices of equal size (except
 for the last slice, which can be less than the slice size provided,
 it is also greater than zero).  The size of each slice depends on the
 MTU determined by the DTLS exchange and SHOULD be the realized MTU
 minus the size of an Image Download Request (Figure 29).
 Note that the Image Download packet and Image Download Request is
 encapsulated in a DTLS header that secures the image download.

6.2.1 Image Download Packet

 The format of an Image Download packet is shown in Figure 28.

Narasimhan, et al. Historic [Page 66] RFC 5413 SLAPP February 2010

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |    Type = 3   |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  RESERVED |M|R|            packet sequence number             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                     image data slice                          ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 28: SLAPP Image Download Packet
 where:
 length: variable
 RESERVED: Unused in this version of SLAPP, MUST be zero (0) on
    transmission and ignored upon receipt.
 M: The "More" bit indicating that the current packet is not the final
    one.
 R: The "Request" bit.  This bit MUST be set to one (1) when the
    packet is the response to a request and zero (0) otherwise.
 packet sequence number: A monotonically increasing counter that
    assigns a unique number to each slice of the image.
 image data slice: A portion of the bootable image.

6.2.2. Image Download Request

 The format of an Image Download Request is shown in Figure 29.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Maj  |  Min  |    Type = 3   |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  RESERVED |M|R|            packet sequence number             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 29: SLAPP Image Download Request Packet
 where:
 length: eight (8) octets

Narasimhan, et al. Historic [Page 67] RFC 5413 SLAPP February 2010

 RESERVED: Unused in this version of SLAPP, MUST be zero on
    transmission and ignored upon receipt.
 M: The "More" bit.  This MUST be equal to the one (1) when negatively
    acknowledging a missed packet and set to zero (0) when indicating
    the end of the Image Download protocol.
 R: the "Request" bit.  This MUST be one in an Image Download Request.
 packet sequence number: The packet sequence number of the missing
    image data slice.

6.2.3. Image Download Process

 The AC will divide the bootable image into a series of slices and
 send each slice as an Image Download packet.  The size of each image
 data slice (and therefore the size of each Image Download packet)
 depends on the MTU of the connection determined during the DTLS
 handshake.  With the transmission of each slice, the AC MUST
 increment the packet sequence number.
 Image Download packets are negatively ACK'd.  An AC MUST NOT assume
 anything about the reception of packets; it sends based upon negative
 ACKs.  One could naively assume that since the packets are sent
 sequentially, that all packets with a sequence number of "n - 1" are
 implicitly ack'd by the receipt of a request for the packet with
 sequence number "n" to be retransmitted.  Such an assumption would be
 incorrect since previous requests could, themselves, have been
 dropped.
 The Image Download process is initiated by the WTP requesting a
 packet with the packet sequence number of zero (0).  The AC sets the
 packet sequence counter for this WTP to one (1) and sends the first
 slice.  The "Request" bit for the first slice sent by the AC MUST be
 set to zero (0) since the first slice was technically not requested.
 The WTP sets a periodic timer that, when it fires, causes the WTP to
 send Image Download Requests for slices that have been missed since
 the last periodic timer had fired.  Since individual Image Download
 packets are not ack'd, the AC MUST NOT set a timer when each one is
 sent.
 If a WTP notices missed image transfer packets -- when the difference
 between the packet sequence number of a received image transfer
 packet and the packet sequence number of the last image transfer
 packet previously received is greater than one -- it will note that
 fact in a bitmask.  When the periodic timer fires, the WTP will
 request the slices that are absent from that bitmask.  Each slice

Narasimhan, et al. Historic [Page 68] RFC 5413 SLAPP February 2010

 will be requested by sending a Download Request with a length of
 eight (8) and indicating the sequence number of the packet requested.
 The AC MUST interleave these retransmissions with packets in the
 sequence.
 Since both sides implicitly agree upon the MTU of the link, the WTP
 will know the slice size that the AC will use during the Image
 Download process.  A dropped packet will therefore result in an
 internal buffer pointer on the WTP being incremented by the slice
 size and the lost packet requested.  When the lost packet is
 received, it can be inserted into the buffer in the space provided by
 the pointer increment when its loss was first detected.  That is,
 loss of packet <n> will result in packet <n> being re-requested and
 when received inserted into the buffer at an offset of <n-1> *
 <slicesize> from the start of the buffer.
 The final packet sent by the AC will not have the "more" bit set, and
 this indicates to the WTP that the end of the image has been
 received.  This final packet is acknowledged by the WTP indicating
 the end of the Image Download process.
 A lost final packet will result in the AC resending the final packet
 again (see Section 4.4).

6.2.4. Image Download State Machine

 The Image Download protocol is a Negotiated Control Protocol defined
 for SLAPP.  Transitions to it come from the "secure" state and
 transitions out of it go to the "acquire" state.  See Figure 3.

6.2.4.1. AC

 The AC's state machine for the Image Download protocol is shown in
 Figure 30.  The AC maintains the following variables for its state
 machine:
 seq_num: The current slice that is being sent.
 nslices: The total number of slices in the image.
 req_num: The number of the slice that was requested.
 more: Whether the "More bit" in the packet should be set.
 starved: A timer that sets the maximum amount of time in which an AC
    will attempt to download an image.

Narasimhan, et al. Historic [Page 69] RFC 5413 SLAPP February 2010

 Note: The symbol "C" indicates an event in a state that results in
 the state remaining the same.
                            |
                            v
                       +----------+
                       |  waiting |
                       +----------+
                            |
                            |   seq_num = 1, more = 1,
                            |   nslices = x, starved = t
              M bit         v
 +----------+  is 0  +-------------+
 | finished |<-------|  received   |<------\
 +----------+        |             |<----\ |
                     +-------------+     | |
  req_num = requested       |            | |
               packet       | M bit is 1 | |
                            V            | |
                       +----------+      | |
           seq_num++, C|  sending |------/ |
           req_num=0   +----------+        |
                            |              |
                         |  |              |
     +-------------+     |  |              |
     | discovering |<----/  |              |
     |             |<----\  |              |
     +-------------+     |  |              |
                         |  v              v
                        +--------+         |
                        | idle   |---------/
                        +--------+
   Figure 30: SLAPP Image Download Protocol State Machine at the AC
 The following states are defined:
 Waiting: When the AC leaves the SLAPP state of "Secure", it enters
    the "Waiting" state of the Image Download protocol.  seq_num is
    set to one (1), more is set to one (1), nslices is set to the
    number of slices in the particular image to download, and starved
    is set to the maximum amount of time the AC will devote to
    downloading a particular image.

Narasimhan, et al. Historic [Page 70] RFC 5413 SLAPP February 2010

 Received: The AC enters this state when it has received an Image
    Download Request.  If the sequence number of the packet is zero
    (0), it sets seq_num to one (1) and transitions to Sending; else,
    if the M bit is set, it sets req_num to the sequence number of the
    request and transitions to Sending; else, (if the M bit is clear)
    it transitions to Finished.
 Sending: The AC is sending a slice to the WTP.  If req_num is equal
    to zero (0), it sends the slice indicated by seq_num and
    increments seq_num.  If req_num is greater than zero (0), it sends
    the slice indicated by req_num and sets req_num to zero (0).  The
    "More" bit in either case is set depending on the value of more.
    As long as no request packets are received Sending transitions to
    Sending.  When seq_num equals nslices "More" is set to zero (0)
    and the state transitions to Idle.  If the starved timer expires,
    the AC transitions to the SLAPP state of Discovering.
 Idle: The AC has sent all the slices in the image and is just waiting
    for requests.  If the starved timer expires the AC transitions to
    the SLAPP state of Discovering.
 Finished: The Image Download protocol has terminated.  The starved
    timer is canceled.

6.2.4.2. WTP

 The WTP's state machine for the Image Download protocol is shown in
 Figure 31.  The WTP maintains the following variables for its state
 machine:
 recv_num: The sequence number of the last received slice.
 req: A bitmask whose length equals the number of slices in the image.
 retry: A timer.
 giveup: A timer.
 final: The sequence number of the last slice.
 Note: The symbol "C" indicates an event in a state that results in
 the state remaining the same.

Narasimhan, et al. Historic [Page 71] RFC 5413 SLAPP February 2010

                             |
                             v
                        +----------+
                        |   init   |    recv_num = 0,
                        +----------+    final = 0, req = 0,
                             |          giveup = t
                             v
  +----------+         +-----------+
  | finished |<------- |  sending  |<-------\
  +----------+         +-----------+        |
                             |              | retry fires
                             v              |
                      +--------------+      |
    bit in req =     C|  receiving   |------/
 seq_num in packet    +--------------+
      is set                 |
                             | giveup fires
                             v
                      +-------------+
                      | discovering |
                      +-------------+
   Figure 31: SLAPP Image Download Protocol State Machine at the WTP
 The following states are defined:
 Init:
    When the WTP leaves the SLAPP state of "Secure", it enters the
    "Init" state of the Image Download protocol.  recv_num, final, and
    the req bitmask are set to zero (0), and the giveup timer is set
    to a suitably large number.  The WTP transitions directly to
    Sending.
 Sending:
    If recv_num is zero (0) the WTP sends a request for a packet with
    sequence number of zero (0) and the "More" bit set to one (1).
    Otherwise, for every unset bit in req between one (1) and
    recv_num, a request packet is sent with the sequence number
    corresponding to the unset bit in req and the "More" bit set to
    more.
    If there are no unset bits in req and final is non-zero, a request
    packet is sent for the sequence number represented by final with
    the "More" bit cleared, giveup is cleared and the state machine
    transitions to Finished.  Otherwise, retry is set to a suitable
    value and the WTP transitions to Receiving.

Narasimhan, et al. Historic [Page 72] RFC 5413 SLAPP February 2010

 Receiving:
    In this state, the WTP receives Image Download packets.  The bit
    in req corresponding to the sequence number in the received packet
    is set, indicating this packet has been received.  If the sequence
    number of the received packet has already been received, the
    packet is silently dropped; otherwise, the data in the packet is
    stored as the indicated slice in a file that represents the
    downloaded image.  If the received packet has the "More" bit
    cleared, final is set to the sequence number in that packet.  When
    the retry timer fires, the WTP transitions to Sending.  If the
    giveup timer fires, the WTP transitions to the SLAPP state of
    Discovering.
 Finished:
    The Image Download protocol has finished.

7. Security Considerations

 This document describes a protocol, SLAPP, which uses a different
 protocol, DTLS, to provide for authentication, key exchange, and bulk
 data encryption of a Negotiated Control Protocol.  Its security
 considerations are therefore those of DTLS.
 The AC creates state upon receipt of an acceptable Discover Request.
 AC implementations of SLAPP SHOULD therefore take measures to protect
 themselves from denial-of-service attacks that attempt to exhaust
 resources on target machines.  These measures could take the form of
 randomly dropping connections when the number of open connections
 reaches a certain threshold.
 The WTP exposes information about itself during the discovery phase.
 Some of this information could not be gleaned by other means.

8. Extensibility to Other Technologies

 The SLAPP protocol can be considered to be a technology-independent
 protocol that can be extended with technology-specific components to
 solve an interoperability problem where a central controller from one
 vendor is expected to control and manage network elements from a
 different vendor.
 While the description of the SLAPP protocol in this document assumes
 that it is meant to solve the multi-vendor interoperability problem,
 as defined in the CAPWAP problem statement [3], splitting the

Narasimhan, et al. Historic [Page 73] RFC 5413 SLAPP February 2010

 solution to two components where technology-dependent control
 protocols are negotiated using a technology-independent framework
 enables the use of SLAPP as the common framework for multiple
 underlying technologies that are vastly different from one another.

9. Informative References

 [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.
 [2]   Yang, L., Zerfos, P., and E. Sadot, "Architecture Taxonomy for
       Control and Provisioning of Wireless Access Points (CAPWAP)",
       RFC 4118, June 2005.
 [3]   O'Hara, B., Calhoun, P., and J. Kempf, "Configuration and
       Provisioning for Wireless Access Points (CAPWAP) Problem
       Statement", RFC 3990, February 2005.
 [4]   Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
       "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
 [5]   Braden, R., Ed., "Requirements for Internet Hosts -
       Communication Layers", STD 3, RFC 1122, October 1989.
 [6]   Rescorla, E. and N. Modadugu, "Datagram Transport Layer
       Security", RFC 4347, April 2006.
 [7]   Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
       Protocol Version 1.2", RFC 5246, August 2008.
 [8]   Modadugu, N. and E. Rescorla, "The Design and Implementation of
       Datagram TLS",
       <http://crypto.stanford.edu/~nagendra/papers/dtls.pdf>.
 [9]   Krishna, P. and D. Husak, "Simple Lightweight RFID Reader
       Protocol", Work in Progress, August 2005.

Narasimhan, et al. Historic [Page 74] RFC 5413 SLAPP February 2010

Authors' Addresses

 Partha Narasimhan
 Aruba Networks
 1322 Crossman Ave
 Sunnyvale, CA  94089
 Phone: +1 408-480-4716
 EMail: partha@arubanetworks.com
 Dan Harkins
 Aruba Networks
 1322 Crossman Ave
 Sunnyvale, CA  94089
 EMail: dharkins@arubanetworks.com
 Subbu Ponnuswamy
 Aruba Networks
 1322 Crossman Ave
 Sunnyvale, CA  94089
 Phone: +1 408-754-1213
 EMail: subbu@arubanetworks.com

Narasimhan, et al. Historic [Page 75]

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