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rfc:rfc6970

Internet Engineering Task Force (IETF) M. Boucadair Request for Comments: 6970 France Telecom Category: Standards Track R. Penno ISSN: 2070-1721 D. Wing

                                                                 Cisco
                                                             July 2013
                   Universal Plug and Play (UPnP)

Internet Gateway Device - Port Control Protocol Interworking Function

                           (IGD-PCP IWF)

Abstract

 This document specifies the behavior of the Universal Plug and Play
 (UPnP) Internet Gateway Device - Port Control Protocol Interworking
 Function (IGD-PCP IWF).  A UPnP IGD-PCP IWF is required to be
 embedded in Customer Premises (CP) routers to allow for transparent
 NAT control in environments where a UPnP IGD is used on the LAN side
 and PCP is used on the external side of the CP router.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 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/rfc6970.

Boucadair, et al. Standards Track [Page 1] RFC 6970 UPnP IGD-PCP IWF July 2013

Copyright Notice

 Copyright (c) 2013 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.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
    1.1. Requirements Language ......................................3
 2. Acronyms ........................................................4
 3. Architecture Model ..............................................4
 4. UPnP IGD-PCP IWF: Overview ......................................6
    4.1. UPnP IGD-PCP: State Variables ..............................6
    4.2. IGD-PCP: Methods ...........................................7
    4.3. UPnP IGD-PCP: Errors .......................................8
 5. Specification of the IGD-PCP IWF ................................9
    5.1. PCP Server Discovery .......................................9
    5.2. Control of the Firewall ...................................10
    5.3. Port Mapping Table ........................................10
    5.4. Interworking Function without NAT in the IGD ..............10
    5.5. NAT Embedded in the IGD ...................................11
    5.6. Creating a Mapping ........................................12
         5.6.1. AddAnyPortMapping() ................................12
         5.6.2. AddPortMapping() ...................................13
    5.7. Listing One or a Set of Mappings ..........................16
    5.8. Delete One or a Set of Mappings: DeletePortMapping() or
         DeletePortMappingRange() ..................................16
    5.9. Renewing a Mapping ........................................19
    5.10. Rapid Recovery ...........................................20
 6. Security Considerations ........................................21
 7. Acknowledgments ................................................21
 8. References .....................................................22
    8.1. Normative References ......................................22
    8.2. Informative References ....................................22

Boucadair, et al. Standards Track [Page 2] RFC 6970 UPnP IGD-PCP IWF July 2013

1. Introduction

 The Port Control Protocol (PCP) specification [RFC6887] discusses the
 implementation of NAT control features that rely upon Carrier Grade
 NAT devices such as a Dual-Stack Lite (DS-Lite) Address Family
 Transition Router (AFTR) [RFC6333] or NAT64 [RFC6146].  In
 environments where a Universal Plug and Play Internet Gateway Device
 (UPnP IGD) is used in the local network, an interworking function
 between the UPnP IGD and PCP is required to be embedded in the IGD
 (see the example illustrated in Figure 1).
                          UPnP IGD-PCP
 UPnP Control             Interworking
    Point                   Function                  PCP Server
      |                       IGD                          |
      |                        |                           |
      |  (1) AddPortMapping()  |                           |
      |----------------------->|                           |
      |                        |   (2) PCP MAP Request     |
      |                        |-------------------------->|
      |                        |                           |
                        Figure 1: Flow Example
 Two configurations are considered within this document:
 o  No NAT function is embedded in the IGD (Section 5.4).  This is
    required, for instance, in DS-Lite or NAT64 deployments.
 o  The IGD embeds a NAT function (Section 5.5).
 The UPnP IGD-PCP Interworking Function (UPnP IGD-PCP IWF) maintains a
 local mapping table that stores all active mappings constructed by
 internal IGD Control Points.  This design choice restricts the amount
 of PCP messages to be exchanged with the PCP server.
 Triggers for deactivating the UPnP IGD-PCP IWF from the IGD and
 relying on a PCP-only mode are out of scope for this document.
 Considerations related to co-existence of the UPnP IGD-PCP
 Interworking Function and a PCP Proxy [PCP-PROXY] are out of scope.

1.1. Requirements Language

 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 [RFC2119].

Boucadair, et al. Standards Track [Page 3] RFC 6970 UPnP IGD-PCP IWF July 2013

2. Acronyms

 This document makes use of the following abbreviations:
    DS-Lite - Dual-Stack Lite
    IGD - Internet Gateway Device
    IGD:1 - UPnP Forum's nomenclature for version 1 of IGD [IGD1]
    IGD:2 - UPnP Forum's nomenclature for version 2 of IGD [IGD2]
    IWF - Interworking Function
    NAT - Network Address Translation
    PCP - Port Control Protocol
    UPnP - Universal Plug and Play

3. Architecture Model

 As a reminder, Figure 2 illustrates the architecture model as adopted
 by the UPnP Forum [IGD2].  In Figure 2, the following UPnP
 terminology is used:
 o  'Client' refers to a host located in the local network.
 o  'IGD Control Point' is a device using UPnP to control an IGD
    (Internet Gateway Device).
 o  'IGD' is a router supporting a UPnP IGD.  It is typically a NAT or
    a firewall.
 o  'Host' is a remote peer reachable in the Internet.
              +-------------+
              | IGD Control |
              |   Point     |-----+
              +-------------+     |   +-----+       +------+
                                  +---|     |       |      |
                                      | IGD |-------| Host |
                                  +---|     |       |      |
              +-------------+     |   +-----+       +------+
              |   Client    |-----+
              +-------------+
                       Figure 2: UPnP IGD Model
 This model is not valid when PCP is used to control, for instance, a
 Carrier Grade NAT (aka Provider NAT) while internal hosts continue to
 use a UPnP IGD.  In such scenarios, Figure 3 shows the updated model.

Boucadair, et al. Standards Track [Page 4] RFC 6970 UPnP IGD-PCP IWF July 2013

 +-------------+
 | IGD Control |
 |   Point     |----+
 +-------------+    |   +-----+      +--------+               +------+
                    +---| IGD-|      |Provider|               |Remote|
                        | PCP |------|  NAT   |--<Internet>---| Host |
                    +---| IWF |      |        |               |      |
 +-------------+    |   +-----+      +--------+               +------+
 | Local Host  |----+
 +-------------+
                      LAN Side  External Side
 <======UPnP IGD==============><=====PCP=====>
               Figure 3: UPnP IGD-PCP Interworking Model
 In the updated model depicted in Figure 3, one or two levels of NAT
 can be encountered in the data path.  Indeed, in addition to the
 Carrier Grade NAT, the IGD may embed a NAT function (Figure 4).
 +-------------+
 | IGD Control |
 |   Point     |----+
 +-------------+    |   +-----+      +--------+               +------+
                    +---| IGD-|      |Provider|               |Remote|
                        | PCP |------|  NAT   |--<Internet>---| Host |
                    +---| IWF |      |        |               |      |
 +-------------+    |   +-----+      +--------+               +------+
 | Local Host  |----+    NAT1           NAT2
 +-------------+
                    Figure 4: Cascaded NAT Scenario
 To ensure successful interworking between a UPnP IGD and PCP, an
 interworking function is embedded in the IGD.  In the model defined
 in Figure 3, all UPnP IGD server-oriented functions, a PCP client
 [RFC6887], and a UPnP IGD-PCP Interworking Function are embedded in
 the IGD.  In the rest of the document, "IGD-PCP IWF" refers to the
 UPnP IGD-PCP Interworking Function, which includes PCP client
 functionality.
 Without the involvement of the IGD-PCP IWF, the IGD Control Point
 would retrieve an external IP address and port number that have
 limited scope and that cannot be used to communicate with hosts
 located beyond NAT2 (i.e., assigned by the IGD, and not those
 assigned by NAT2 as depicted in Figure 4).
 The UPnP IGD-PCP IWF is responsible for generating a well-formed PCP
 message from a received UPnP IGD message, and vice versa.

Boucadair, et al. Standards Track [Page 5] RFC 6970 UPnP IGD-PCP IWF July 2013

4. UPnP IGD-PCP IWF: Overview

 Three tables are provided to specify the correspondence between a
 UPnP IGD and PCP:
 (1)  Section 4.1 provides the mapping between WANIPConnection state
      variables and PCP parameters;
 (2)  Section 4.2 focuses on the correspondence between supported
      methods;
 (3)  Section 4.3 lists the PCP error messages and their corresponding
      IGD error messages.
 Note that some enhancements have been integrated in WANIPConnection,
 as documented in [IGD2].

4.1. UPnP IGD-PCP: State Variables

 Below are listed only the UPnP IGD state variables applicable to the
 IGD-PCP IWF:
 ExternalIPAddress:  External IP Address
    Read-only variable with the value from the last PCP response, or
    the empty string if none was received yet.  This state is stored
    on a per-IGD-Control-Point basis.
 PortMappingNumberOfEntries:  Managed locally by the UPnP IGD-PCP IWF.
 PortMappingEnabled:
    PCP does not support deactivating the dynamic NAT mapping, since
    the initial goal of PCP is to ease the traversal of Carrier Grade
    NAT.  Supporting such per-subscriber function may overload the
    Carrier Grade NAT.
    Only "1" is allowed: i.e., the UPnP IGD-PCP Interworking Function
    MUST send back an error if a value different from 1 is signaled.
 PortMappingLeaseDuration:  Requested Mapping Lifetime
    In IGD:1 [IGD1], the value 0 means infinite; in IGD:2, it is
    remapped to the IGD maximum of 604800 seconds [IGD2].  PCP allows
    for a maximum value of 4294967296 seconds.
    The UPnP IGD-PCP Interworking Function simulates long and even
    infinite lifetimes using renewals (see Section 5.9).  The behavior
    of the UPnP IGD-PCP IWF in the case of a failing renewal is
    currently undefined (see Section 5.9).

Boucadair, et al. Standards Track [Page 6] RFC 6970 UPnP IGD-PCP IWF July 2013

    IGD:1 doesn't define the behavior in the case of state loss; IGD:2
    doesn't require that state be kept in stable storage, i.e., to
    allow the state to survive resets/reboots.  The UPnP IGD-PCP
    Interworking Function MUST support IGD:2 behavior.
 RemoteHost:  Remote Peer IP Address
    Note that IGD:2 allows a domain name, which has to be resolved to
    an IP address.  Mapped to the Remote Peer IP Address field of the
    FILTER option.
 ExternalPort:  External Port Number
    Mapped to the Suggested External Port field in MAP messages.
 InternalPort:  Internal Port Number
    Mapped to the Internal Port field in MAP messages.
 PortMappingProtocol:  Protocol
    Mapped to the Protocol field in MAP messages.  Note that a UPnP
    IGD only supports TCP and UDP.
 InternalClient:  Internal IP Address
    Note that IGD:2 allows a domain name, which has to be resolved to
    an IP address.  Mapped to the Internal IP Address field of the
    THIRD_PARTY option.
 PortMappingDescription:  Not supported in base PCP.
    If the local PCP client supports a PCP option to convey the
    description (e.g., [PCP-DESCR-OPT]), this option SHOULD be used to
    relay the mapping description.
 SystemUpdateID (IGD:2 only):  Managed locally by the UPnP IGD-PCP
    IWF.
 A_ARG_TYPE_PortListing (IGD:2 only):  Managed locally by the UPnP
    IGD-PCP IWF.

4.2. IGD-PCP: Methods

 IGD:1 and IGD:2 methods applicable to the UPnP IGD-PCP Interworking
 Function are both listed here.
 GetGenericPortMappingEntry():  This request is not relayed to the PCP
    server.
    The IGD-PCP Interworking Function maintains a list of active
    mappings instantiated in the PCP server by internal hosts.  See
    Section 5.7 for more information.

Boucadair, et al. Standards Track [Page 7] RFC 6970 UPnP IGD-PCP IWF July 2013

 GetSpecificPortMappingEntry():  MAP with PREFER_FAILURE option.
    This request is relayed to the PCP server by issuing a MAP request
    with the PREFER_FAILURE option.  It is RECOMMENDED to use a short
    lifetime (e.g., 60 seconds).
 AddPortMapping():  MAP
    See Section 5.6.2.
 AddAnyPortMapping() (IGD:2 only):  MAP
    See Section 5.6.1.
 DeletePortMapping():  MAP with Requested Lifetime set to 0.
    See Section 5.8.
 DeletePortMappingRange() (IGD:2 only):  MAP with Requested Lifetime
    set to 0.
    Individual requests are issued by the IGD-PCP IWF.  See
    Section 5.8 for more details.
 GetExternalIPAddress():  MAP
    This can be learned from any active mapping.  If there are no
    active mappings, the IGD-PCP IWF MAY request a short-lived mapping
    (e.g., to the Discard service (TCP/9 or UDP/9) or some other
    port).  However, once that mapping expires, a subsequent implicit
    or explicit dynamic mapping might be mapped to a different
    external IP address.  See Section 11.6 of [RFC6887] for more
    discussion.
 GetListOfPortMappings():  See Section 5.7 for more information.
    The IGD-PCP Interworking Function maintains a list of active
    mappings instantiated in the PCP server.  The IGD-PCP Interworking
    Function handles this request locally.

4.3. UPnP IGD-PCP: Errors

 This section lists PCP error codes and the corresponding UPnP IGD
 codes.  Error codes specific to IGD:2 are tagged accordingly.
 1 UNSUPP_VERSION:  501 "ActionFailed"
 2 NOT_AUTHORIZED:  IGD:1 718 "ConflictInMappingEntry" / IGD:2 606
    "Action not authorized"
 3 MALFORMED_REQUEST:  501 "ActionFailed"

Boucadair, et al. Standards Track [Page 8] RFC 6970 UPnP IGD-PCP IWF July 2013

 4 UNSUPP_OPCODE:  501 "ActionFailed"
    [RFC6887] allows the PCP server to be configured to disable
    support for the MAP Opcode, but the IGD-PCP IWF cannot work in
    this situation.
 5 UNSUPP_OPTION:  501 "ActionFailed"
    This error code can be received if PREFER_FAILURE is not supported
    on the PCP server.  Note that PREFER_FAILURE is not mandatory to
    support, but AddPortMapping() cannot be implemented without it.
 6 MALFORMED_OPTION:  501 "ActionFailed"
 7 NETWORK_FAILURE:  501 "ActionFailed"
 8 NO_RESOURCES:  IGD:1 501 "ActionFailed" / IGD:2 728
    "NoPortMapsAvailable"
    Cannot be distinguished from USER_EX_QUOTA.
 9 UNSUPP_PROTOCOL:  501 "ActionFailed"
 10 USER_EX_QUOTA:  IGD:1 501 "ActionFailed" / IGD:2 728
    "NoPortMapsAvailable"
    Cannot be distinguished from NO_RESOURCES.
 11 CANNOT_PROVIDE_EXTERNAL:  718 "ConflictInMappingEntry" (see
    Section 5.6.2) or 714 "NoSuchEntryInArray" (see Section 5.8).
 12 ADDRESS_MISMATCH:  501 "ActionFailed"
 13 EXCESSIVE_REMOTE_PEERS:  501 "ActionFailed"

5. Specification of the IGD-PCP IWF

 This section covers scenarios with or without NAT in the IGD.
 This specification assumes that the PCP server is configured to
 accept the MAP Opcode.
 The IGD-PCP IWF handles the "Mapping Nonce" the same way as any PCP
 client [RFC6887].

5.1. PCP Server Discovery

 The IGD-PCP IWF implements one of the discovery methods identified in
 [RFC6887] (e.g., DHCP [PCP-DHCP-OPT]).  The IGD-PCP Interworking
 Function behaves as a PCP client when communicating with provisioned
 PCP server(s).

Boucadair, et al. Standards Track [Page 9] RFC 6970 UPnP IGD-PCP IWF July 2013

 If no IPv4 address/IPv6 prefix is assigned to the IGD or the IGD is
 unable to determine whether it should contact an upstream PCP server,
 the IGD-PCP Interworking Function MUST NOT be invoked.
 If the IGD determines that it should establish communication with an
 upstream PCP server (e.g., because of DHCP configuration or having
 previously communicated with a PCP server), a "501 ActionFailed"
 error message is returned to the requesting IGD Control Point if the
 IGD-PCP IWF fails to establish communication with that PCP server.
 Note that the IGD-PCP IWF proceeds to PCP message validation and
 retransmission the same way as any PCP client [RFC6887].

5.2. Control of the Firewall

 In order to configure security policies to be applied to inbound and
 outbound traffic, a UPnP IGD can be used to control a local firewall
 engine.  No IGD-PCP IWF is therefore required for that purpose.
 The use of the IGD-PCP IWF to control an upstream PCP-controlled
 firewall is out of scope for this document.

5.3. Port Mapping Table

 The IGD-PCP IWF MUST store locally all the mappings instantiated by
 internal IGD Control Points in the PCP server.  All mappings SHOULD
 be stored in permanent storage.
 Upon receipt of a PCP MAP response from the PCP server, the IGD-PCP
 Interworking Function MUST extract the enclosed mapping and MUST
 store it in the local mapping table.  The local mapping table is an
 image of the mapping table as maintained by the PCP server for a
 given subscriber.
 Each mapping entry stored in the local mapping table is associated
 with a lifetime as discussed in [RFC6887].  Additional considerations
 specific to the IGD-PCP Interworking Function are discussed in
 Section 5.9.

5.4. Interworking Function without NAT in the IGD

 When no NAT is embedded in the IGD, the contents of received
 WANIPConnection and PCP messages are not altered by the IGD-PCP
 Interworking Function (i.e., the contents of WANIPConnection messages
 are mapped to PCP messages (and mapped back), according to
 Section 4.1).

Boucadair, et al. Standards Track [Page 10] RFC 6970 UPnP IGD-PCP IWF July 2013

5.5. NAT Embedded in the IGD

 When NAT is embedded in the IGD, the IGD-PCP IWF updates the contents
 of mapping messages received from the IGD Control Point.  These
 messages will contain an IP address and/or port number that belong to
 an internal host.  The IGD-PCP IWF MUST update such messages with the
 IP address and/or port number belonging to the external interface of
 the IGD (i.e., after the NAT1 operation as depicted in Figure 4).
 The IGD-PCP IWF intercepts all WANIPConnection messages issued by the
 IGD Control Point.  For each such message, the IGD-PCP IWF then
 generates one or more corresponding requests (see Sections 4.1, 4.2,
 and 4.3) and sends them to the provisioned PCP server.
 Each request sent by the IGD-PCP IWF to the PCP server MUST reflect
 the mapping information as enforced in the first NAT.  Particularly,
 the internal IP address and/or port number of the requests are
 replaced with the IP address and/or port number as assigned by the
 NAT of the IGD.  For the reverse path, the IGD-PCP IWF intercepts PCP
 response messages and generates WANIPConnection response messages.
 The contents of the generated WANIPConnection response messages are
 set as follows:
 o  The internal IP address and/or port number as initially set by the
    IGD Control Point and stored in the IGD NAT are used to update the
    corresponding fields in received PCP responses.
 o  The external IP address and port number are not altered by the
    IGD-PCP Interworking Function.
 o  The NAT mapping entry in the IGD is updated with the result of
    each PCP request.
 The lifetime of the mappings instantiated in the IGD SHOULD be the
 one assigned by the terminating PCP server.  In any case, the
 lifetime MUST NOT be lower than the one assigned by the terminating
 PCP server.

Boucadair, et al. Standards Track [Page 11] RFC 6970 UPnP IGD-PCP IWF July 2013

5.6. Creating a Mapping

 Two methods can be used to create a mapping: AddAnyPortMapping() and
 AddPortMapping().

5.6.1. AddAnyPortMapping()

 When an IGD Control Point issues an AddAnyPortMapping() call, this
 request is received by the IGD.  The request is then relayed to the
 IGD-PCP IWF, which generates a PCP MAP request (see Section 4.1 for
 mapping between WANIPConnection and PCP parameters).
 If the IGD-PCP IWF fails to send the MAP request to its PCP server,
 it follows the behavior defined in Section 5.1.
 Upon receipt of a PCP MAP response from the PCP server, the
 corresponding UPnP IGD method is returned to the requesting IGD
 Control Point (the contents of the messages follow the
 recommendations listed in Section 5.5 or Section 5.4, according to
 the deployed scenario).  A flow example is depicted in Figure 5.
 If a PCP error is received from the PCP server, a corresponding
 WANIPConnection error code (see Section 4.3) is generated by the
 IGD-PCP IWF and sent to the requesting IGD Control Point.  If a
 short-lifetime error is returned (e.g., NETWORK_FAILURE,
 NO_RESOURCES), the PCP IWF MAY resend the same request to the PCP
 server after 30 seconds.  If a negative answer is received, the error
 is then relayed to the requesting IGD Control Point.
    Discussion: Some applications (e.g., uTorrent, Vuze, eMule) wait
    90 seconds or more for a response after sending a UPnP request.
    If a short-lifetime error occurs, resending the request may lead
    to a positive response from the PCP server.  IGD Control Points
    are therefore not aware of transient errors.

Boucadair, et al. Standards Track [Page 12] RFC 6970 UPnP IGD-PCP IWF July 2013

                             UPnP-PCP
 UPnP Control              Interworking
    Point                    Function                    PCP Server
      |                         |                             |
      | (1) AddAnyPortMapping() |                             |
      |    ExternalPort=8080    |                             |
      |------------------------>|                             |
      |                         |   (2) PCP MAP Request       |
      |                         |Suggested External Port=8080 |
      |                         |---------------------------->|
      |                         |                             |
      |                         |   (3) PCP MAP Response      |
      |                         | Assigned External Port=6598 |
      |                         |<----------------------------|
      | (4) AddAnyPortMapping() |                             |
      |    ReservedPort=6598    |                             |
      |<------------------------|                             |
              Figure 5: Flow Example: AddAnyPortMapping()

5.6.2. AddPortMapping()

 A dedicated option called "PREFER_FAILURE" is defined in [RFC6887] to
 toggle the behavior in a PCP request message.  This option is
 inserted by the IGD-PCP IWF when issuing its requests to the PCP
 server only if a specific external port is requested by the IGD
 Control Point.
 Upon receipt of AddPortMapping() from an IGD Control Point, the
 IGD-PCP IWF MUST generate a PCP MAP request with all requested
 mapping information as indicated by the IGD Control Point if no NAT
 is embedded in the IGD or updated as specified in Section 5.5.  In
 addition, the IGD-PCP IWF MUST insert a PREFER_FAILURE option in the
 generated PCP request.
 If the IGD-PCP IWF fails to send the MAP request to its PCP server,
 it follows the behavior defined in Section 5.1.
 If the requested external port is not available, the PCP server will
 send a CANNOT_PROVIDE_EXTERNAL error response:
 1.  If a short-lifetime error is returned, the IGD-PCP IWF MAY resend
     the same request to the PCP server after 30 seconds without
     relaying the error to the IGD Control Point.  The IGD-PCP IWF MAY
     repeat this process until a positive answer is received or some
     maximum retry limit is reached.  When the maximum retry limit is
     reached, the IGD-PCP IWF relays a negative message to the IGD
     Control Point with ConflictInMappingEntry as the error code.

Boucadair, et al. Standards Track [Page 13] RFC 6970 UPnP IGD-PCP IWF July 2013

     The maximum retry limit is implementation-specific; its default
     value is 2.
 2.  If a long-lifetime error is returned, the IGD-PCP IWF relays a
     negative message to the IGD Control Point with
     ConflictInMappingEntry as the error code.
 The IGD Control Point may issue a new request with a different
 requested external port number.  This process is typically repeated
 by the IGD Control Point until a positive answer is received or some
 maximum retry limit is reached.
 If the PCP server is able to create or renew a mapping with the
 requested external port, it sends a positive response to the IGD-PCP
 IWF.  Upon receipt of the response from the PCP server, the IGD-PCP
 IWF stores the returned mapping in its local mapping table and sends
 the corresponding positive answer to the requesting IGD Control
 Point.  This answer terminates the exchange.
 Figure 6 shows an example of the flow exchange that occurs when the
 PCP server satisfies the request from the IGD-PCP IWF.  Figure 7
 shows the message exchange when the requested external port is not
 available.
                            UPnP-PCP
 UPnP Control             Interworking
    Point                   Function                    PCP Server
      |                        |                             |
      |  (1) AddPortMapping()  |                             |
      |    ExternalPort=8080   |                             |
      |----------------------->|                             |
      |                        |   (2) PCP MAP Request       |
      |                        |Suggested External Port=8080 |
      |                        |       PREFER_FAILURE        |
      |                        |---------------------------->|
      |                        |                             |
      |                        |   (3) PCP MAP Response      |
      |                        | Assigned External Port=8080 |
      |                        |<----------------------------|
      |  (4) AddPortMapping()  |                             |
      |    ExternalPort=8080   |                             |
      |<-----------------------|                             |
               Figure 6: Flow Example (Positive Answer)

Boucadair, et al. Standards Track [Page 14] RFC 6970 UPnP IGD-PCP IWF July 2013

                            UPnP-PCP
 UPnP Control             Interworking
    Point                   Function                    PCP Server
      |                        |                             |
      |  (1) AddPortMapping()  |                             |
      |    ExternalPort=8080   |                             |
      |----------------------->|                             |
      |                        |   (2) PCP MAP Request       |
      |                        |Suggested External Port=8080 |
      |                        |       PREFER_FAILURE        |
      |                        |---------------------------->|
      |                        |   (3) PCP MAP Response      |
      |                        |   CANNOT_PROVIDE_EXTERNAL   |
      |                        |<----------------------------|
      |      (4) Error:        |                             |
      | ConflictInMappingEntry |                             |
      |<-----------------------|                             |
      |  (5) AddPortMapping()  |                             |
      |    ExternalPort=5485   |                             |
      |----------------------->|                             |
      |                        |   (6) PCP MAP Request       |
      |                        |Suggested External Port=5485 |
      |                        |       PREFER_FAILURE        |
      |                        |---------------------------->|
      |                        |   (7) PCP MAP Response      |
      |                        |   CANNOT_PROVIDE_EXTERNAL   |
      |                        |<----------------------------|
      |      (8) Error:        |                             |
      | ConflictInMappingEntry |                             |
      |<-----------------------|                             |
                               ....
      |  (a) AddPortMapping()  |                             |
      |    ExternalPort=6591   |                             |
      |----------------------->|                             |
      |                        |   (b) PCP MAP Request       |
      |                        |Suggested External Port=6591 |
      |                        |       PREFER_FAILURE        |
      |                        |---------------------------->|
      |                        |   (c) PCP MAP Response      |
      |                        |   CANNOT_PROVIDE_EXTERNAL   |
      |                        |<----------------------------|
      |      (d) Error:        |                             |
      | ConflictInMappingEntry |                             |
      |<-----------------------|                             |
               Figure 7: Flow Example (Negative Answer)

Boucadair, et al. Standards Track [Page 15] RFC 6970 UPnP IGD-PCP IWF July 2013

    Note: According to some experiments, some UPnP 1.0 Control Point
    implementations, e.g., uTorrent, simply try the same external port
    a number of times (usually 4 times) and then fail if the port is
    in use.  Also note that some applications use
    GetSpecificPortMappingEntry() to determine whether a mapping
    exists.

5.7. Listing One or a Set of Mappings

 In order to list active mappings, an IGD Control Point may issue
 GetGenericPortMappingEntry(), GetSpecificPortMappingEntry(), or
 GetListOfPortMappings().
 GetGenericPortMappingEntry() and GetListOfPortMappings() methods MUST
 NOT be proxied to the PCP server, since a local mapping is maintained
 by the IGD-PCP IWF.
 Upon receipt of GetSpecificPortMappingEntry() from an IGD Control
 Point, the IGD-PCP IWF MUST check first to see if the external port
 number is used by the requesting IGD Control Point.  If the external
 port is already in use by the requesting IGD Control Point, the
 IGD-PCP IWF MUST send back the mapping entry matching the request.
 If not, the IGD-PCP IWF MUST relay to the PCP server a MAP request,
 with short lifetime (e.g., 60 seconds), including a PREFER_FAILURE
 option.  If the IGD-PCP IWF fails to send the MAP request to its PCP
 server, it follows the behavior defined in Section 5.1.  If the
 requested external port is in use, a PCP error message will be sent
 by the PCP server to the IGD-PCP IWF indicating
 CANNOT_PROVIDE_EXTERNAL as the error cause.  Then, the IGD-PCP IWF
 relays a negative message to the IGD Control Point.  If the port is
 not in use, the mapping will be created by the PCP server and a
 positive response will be sent back to the IGD-PCP IWF.  Once
 received by the IGD-PCP IWF, it MUST relay a negative message to the
 IGD Control Point indicating NoSuchEntryInArray as the error code so
 that the IGD Control Point knows the queried mapping doesn't exist.

5.8. Delete One or a Set of Mappings: DeletePortMapping() or

    DeletePortMappingRange()
 An IGD Control Point requests the deletion of one or a list of
 mappings by issuing DeletePortMapping() or DeletePortMappingRange().
 In IGD:2, we assume that the IGD applies the appropriate security
 policies to determine whether a Control Point has the rights to
 delete one or a set of mappings.  When authorization fails, the "606
 Action Not Authorized" error code is returned to the requesting
 Control Point.

Boucadair, et al. Standards Track [Page 16] RFC 6970 UPnP IGD-PCP IWF July 2013

 When DeletePortMapping() or DeletePortMappingRange() is received by
 the IGD-PCP IWF, it first checks if the requested mappings to be
 removed are present in the local mapping table.  If no mapping
 matching the request is found in the local table, an error code is
 sent back to the IGD Control Point: "714 NoSuchEntryInArray" for
 DeletePortMapping() or "730 PortMappingNotFound" for
 DeletePortMappingRange().
 Figure 8 shows an example of an IGD Control Point asking to delete a
 mapping that is not instantiated in the local table of the IWF.
                             UPnP-PCP
 UPnP Control              Interworking
    Point                    Function                  PCP Server
      |                         |                           |
      | (1) DeletePortMapping() |                           |
      |------------------------>|                           |
      |                         |                           |
      |       (2) Error:        |                           |
      |    NoSuchEntryInArray   |                           |
      |<------------------------|                           |
      |                         |                           |
                 Figure 8: Local Delete (IGD-PCP IWF)
 If a mapping matches in the local table, a PCP MAP delete request is
 generated.  If no NAT is enabled in the IGD, the IGD-PCP IWF uses the
 input arguments as included in DeletePortMapping().  If a NAT is
 enabled in the IGD, the IGD-PCP IWF instead uses the corresponding IP
 address and port number as assigned by the local NAT.
 If the IGD-PCP IWF fails to send the MAP request to its PCP server,
 it follows the behavior defined in Section 5.1.
 When a positive answer is received from the PCP server, the IGD-PCP
 IWF updates its local mapping table (i.e., removes the corresponding
 entry) and notifies the IGD Control Point of the result of the
 removal operation.  Once the PCP MAP delete request is received by
 the PCP server, it removes the corresponding entry.  A PCP MAP
 SUCCESS response is sent back if the removal of the corresponding
 entry was successful; if not, a PCP error message containing the
 corresponding error cause (see Section 4.3) is sent back to the
 IGD-PCP IWF.

Boucadair, et al. Standards Track [Page 17] RFC 6970 UPnP IGD-PCP IWF July 2013

 If DeletePortMappingRange() is used, the IGD-PCP IWF does a lookup in
 its local mapping table to retrieve individual mappings, instantiated
 by the requesting Control Point (i.e., authorization checks), that
 match the signaled port range (i.e., the external port is within the
 "StartPort" and "EndPort" arguments of DeletePortMappingRange()).  If
 no mapping is found, the "730 PortMappingNotFound" error code is sent
 to the IGD Control Point (Figure 9).  If one or more mappings are
 found, the IGD-PCP IWF generates individual PCP MAP delete requests
 corresponding to these mappings (see the example shown in Figure 10).
 The IGD-PCP IWF MAY send a positive answer to the requesting IGD
 Control Point without waiting to receive all the answers from the PCP
 server.
                                  UPnP-PCP
 UPnP Control                   Interworking
    Point                         Function                 PCP Server
      |                              |                          |
      | (1) DeletePortMappingRange() |                          |
      |       StartPort=8596         |                          |
      |       EndPort  =9000         |                          |
      |       Protocol =UDP          |                          |
      |----------------------------->|                          |
      |                              |                          |
      |       (2) Error:             |                          |
      |   PortMappingNotFound        |                          |
      |<-----------------------------|                          |
      |                              |                          |
       Figure 9: Flow Example: Error Encountered when Processing
                       DeletePortMappingRange()

Boucadair, et al. Standards Track [Page 18] RFC 6970 UPnP IGD-PCP IWF July 2013

 Figure 10 illustrates the exchanges that occur when the IWF receives
 DeletePortMappingRange().  In this example, only two mappings having
 the external port number in the 6000-6050 range are maintained in the
 local table.  The IWF issues two MAP requests to delete these
 mappings.
                                  UPnP-PCP
 UPnP Control                   Interworking
    Point                         Function                 PCP Server
      |                              |                          |
      | (1) DeletePortMappingRange() |                          |
      |     StartPort=6000           |                          |
      |     EndPort  =6050           |                          |
      |     Protocol =UDP            |                          |
      |----------------------------->|                          |
      |                              |                          |
      |                              |   (2a) PCP MAP Request   |
      |                              |       Protocol=UDP       |
      |                              |   internal-ip-address    |
      |                              |      internal-port       |
      |                              |   external-ip-address    |
      |                              |   external-port=6030     |
      |                              |   Requested-lifetime=0   |
      |                              |------------------------->|
      |                              |                          |
      |                              |   (2b) PCP MAP Request   |
      |                              |       Protocol=UDP       |
      |                              |   internal-ip-address    |
      |                              |      internal-port       |
      |                              |   external-ip-address    |
      |                              |   external-port=6045     |
      |                              |   Requested-lifetime=0   |
      |                              |------------------------->|
      |                              |                          |
      |     (3) Positive answer      |                          |
      |<-----------------------------|                          |
      |                              |                          |
            Figure 10: Example of DeletePortMappingRange()

5.9. Renewing a Mapping

 Because of the incompatibility of mapping lifetimes between a UPnP
 IGD and PCP, the IGD-PCP IWF MUST simulate long and even infinite
 lifetimes.  Indeed, for requests having a requested infinite
 PortMappingLeaseDuration, the IGD-PCP IWF MUST set the Requested
 Lifetime of the corresponding PCP request to 4294967296.  If
 PortMappingLeaseDuration is not infinite, the IGD-PCP IWF MUST set

Boucadair, et al. Standards Track [Page 19] RFC 6970 UPnP IGD-PCP IWF July 2013

 the Requested Lifetime of the corresponding PCP request to the same
 value as PortMappingLeaseDuration.  Furthermore, the IGD-PCP
 Interworking Function MUST maintain an additional timer set to the
 initial requested PortMappingLeaseDuration.  Upon receipt of a
 positive answer from the PCP server, the IGD-PCP IWF relays the
 corresponding UPnP IGD response to the requesting IGD Control Point
 with PortMappingLeaseDuration set to the same value as that of the
 initial request.  Then, the IGD-PCP IWF MUST periodically renew the
 constructed PCP mapping until the expiry of PortMappingLeaseDuration.
 Responses received when renewing the mapping MUST NOT be relayed to
 the IGD Control Point.
 If an error is encountered during mapping renewal, the IGD-PCP
 Interworking Function has no means of informing the IGD Control Point
 of the error.

5.10. Rapid Recovery

 When the IGD-PCP IWF is co-located with the DHCP server, the state
 maintained by the IGD-PCP IWF MUST be updated using the state in the
 local DHCP server.  Particularly, if an IP address expires or is
 released by an internal host, the IGD-PCP IWF MUST delete all the
 mappings bound to that internal IP address.
 Upon change of the external IP address of the IGD-PCP IWF, the
 IGD-PCP IWF MAY renew the mappings it maintained.  This can be
 achieved only if a full state table is maintained by the IGD-PCP IWF.
 If the port quota is not exceeded in the PCP server, the IGD-PCP IWF
 will receive a new external IP address and port numbers.  The IGD-PCP
 IWF has no means of notifying internal IGD Control Points of the
 change of the external IP address and port numbers.  Stale mappings
 will be maintained by the PCP server until their lifetime expires.
    Note: If an address change occurs, protocols that are sensitive to
    address changes (e.g., TCP) will experience disruption.
 [RFC6887] defines a procedure for the PCP server to notify PCP
 clients of changes related to the mappings it maintains.  When an
 unsolicited ANNOUNCE is received, the IGD-PCP IWF makes one or more
 MAP requests with the PREFER_FAILURE option to re-install its
 mappings.  If the PCP server cannot create the requested mappings
 (signaled with the CANNOT_PROVIDE_EXTERNAL error response), the
 IGD-PCP IWF has no means of notifying internal IGD Control Points of
 any changes of the external IP address and port numbers.

Boucadair, et al. Standards Track [Page 20] RFC 6970 UPnP IGD-PCP IWF July 2013

 Unsolicited PCP MAP responses received from a PCP server are handled
 as any normal MAP response.  If a response indicates that the
 external IP address or port has changed, the IGD-PCP IWF has no means
 of notifying the internal IGD Control Point of this change.
 Further analysis of PCP failure scenarios for the IGD-PCP
 Interworking Function are discussed in [PCP-FAILURE].

6. Security Considerations

 IGD:2 access control requirements and authorization levels SHOULD be
 applied by default [IGD2].  When IGD:2 is used, operation on behalf
 of a third party SHOULD be allowed only if authentication and
 authorization are used [IGD2].  When only IGD:1 is available,
 operation on behalf of a third party SHOULD NOT be allowed.
 This document defines a procedure to create PCP mappings for third-
 party devices belonging to the same subscriber.  The means for
 preventing a malicious user from creating mappings on behalf of a
 third party must be enabled as discussed in Section 13.1 of
 [RFC6887].  In particular, the THIRD_PARTY option MUST NOT be enabled
 unless the network on which the PCP messages are to be sent is fully
 trusted -- for example, access control lists (ACLs) installed on the
 PCP client, the PCP server, and the network between them, so that
 those ACLs allow only communications from a trusted PCP client to the
 PCP server.
 An IGD Control Point that issues AddPortMapping(),
 AddAnyPortMapping(), or GetSpecificPortMappingEntry() requests in a
 shorter time frame will create a lot of mapping entries on the PCP
 server.  The means for avoiding the exhaustion of port resources
 (e.g., port quota, as discussed in Section 17.2 of [RFC6887]) SHOULD
 be enabled.
 The security considerations discussed in [RFC6887] and [Sec_DCP]
 should be taken into account.

7. Acknowledgments

 The authors would like to thank F. Fontaine, C. Jacquenet, X. Deng,
 G. Montenegro, D. Thaler, R. Tirumaleswar, P. Selkirk, T. Lemon,
 V. Gurbani, and P. Yee for their review and comments.
 F. Dupont contributed to previous versions of this document.  Thanks
 go to him for his thorough reviews and contributions.

Boucadair, et al. Standards Track [Page 21] RFC 6970 UPnP IGD-PCP IWF July 2013

8. References

8.1. Normative References

 [IGD1]     UPnP Forum, "WANIPConnection:1 Service Template
            Version 1.01", November 2001, <http://upnp.org/specs/
            gw/UPnP-gw-WANIPConnection-v1-Service.pdf>.
 [IGD2]     UPnP Forum, "WANIPConnection:2 Service", September 2010,
            <http://upnp.org/specs/gw/
            UPnP-gw-WANIPConnection-v2-Service.pdf>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
            Selkirk, "Port Control Protocol (PCP)", RFC 6887,
            April 2013.

8.2. Informative References

 [PCP-DESCR-OPT]
            Boucadair, M., Penno, R., and D. Wing, "PCP Description
            Option", Work in Progress, May 2013.
 [PCP-DHCP-OPT]
            Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
            the Port Control Protocol (PCP)", Work in Progress,
            March 2013.
 [PCP-FAILURE]
            Boucadair, M. and R. Penno, "Analysis of Port Control
            Protocol (PCP) Failure Scenarios", Work in Progress,
            May 2013.
 [PCP-PROXY]
            Boucadair, M., Penno, R., and D. Wing, "Port Control
            Protocol (PCP) Proxy Function", Work in Progress,
            June 2013.
 [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
            NAT64: Network Address and Protocol Translation from IPv6
            Clients to IPv4 Servers", RFC 6146, April 2011.

Boucadair, et al. Standards Track [Page 22] RFC 6970 UPnP IGD-PCP IWF July 2013

 [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee,
            "Dual-Stack Lite Broadband Deployments Following IPv4
            Exhaustion", RFC 6333, August 2011.
 [Sec_DCP]  UPnP Forum, "Device Protection:1 Service", February 2011,
            <http://upnp.org/specs/gw/
            UPnP-gw-DeviceProtection-v1-Service.pdf>.

Authors' Addresses

 Mohamed Boucadair
 France Telecom
 Rennes  35000
 France
 EMail: mohamed.boucadair@orange.com
 Reinaldo Penno
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, California  95134
 USA
 EMail: repenno@cisco.com
 Dan Wing
 Cisco Systems, Inc.
 170 West Tasman Drive
 San Jose, California  95134
 USA
 EMail: dwing@cisco.com

Boucadair, et al. Standards Track [Page 23]

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