GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc5085

Network Working Group T. Nadeau, Ed. Request for Comments: 5085 C. Pignataro, Ed. Category: Standards Track Cisco Systems, Inc.

                                                         December 2007
    Pseudowire Virtual Circuit Connectivity Verification (VCCV):
                 A Control Channel for Pseudowires

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 This document describes Virtual Circuit Connectivity Verification
 (VCCV), which provides a control channel that is associated with a
 pseudowire (PW), as well as the corresponding operations and
 management functions (such as connectivity verification) to be used
 over that control channel.  VCCV applies to all supported access
 circuit and transport types currently defined for PWs.

Nadeau & Pignataro Standards Track [Page 1] RFC 5085 PW VCCV December 2007

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1.  Specification of Requirements  . . . . . . . . . . . . . .  5
 2.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . . . .  5
 3.  Overview of VCCV . . . . . . . . . . . . . . . . . . . . . . .  6
 4.  CC Types and CV Types  . . . . . . . . . . . . . . . . . . . .  8
 5.  VCCV Control Channel for MPLS PWs  . . . . . . . . . . . . . . 10
   5.1.  VCCV Control Channel Types for MPLS  . . . . . . . . . . . 10
     5.1.1.  In-Band VCCV (Type 1)  . . . . . . . . . . . . . . . . 11
     5.1.2.  Out-of-Band VCCV (Type 2)  . . . . . . . . . . . . . . 12
     5.1.3.  TTL Expiry VCCV (Type 3) . . . . . . . . . . . . . . . 12
   5.2.  VCCV Connectivity Verification Types for MPLS  . . . . . . 13
     5.2.1.  ICMP Ping  . . . . . . . . . . . . . . . . . . . . . . 13
     5.2.2.  MPLS LSP Ping  . . . . . . . . . . . . . . . . . . . . 13
   5.3.  VCCV Capability Advertisement for MPLS PWs . . . . . . . . 13
     5.3.1.  VCCV Capability Advertisement LDP Sub-TLV  . . . . . . 14
 6.  VCCV Control Channel for L2TPv3/IP PWs . . . . . . . . . . . . 15
   6.1.  VCCV Control Channel Type for L2TPv3 . . . . . . . . . . . 16
   6.2.  VCCV Connectivity Verification Type for L2TPv3 . . . . . . 17
     6.2.1.  L2TPv3 VCCV using ICMP Ping  . . . . . . . . . . . . . 17
   6.3.  L2TPv3 VCCV Capability Advertisement for L2TPv3  . . . . . 17
     6.3.1.  L2TPv3 VCCV Capability AVP . . . . . . . . . . . . . . 17
 7.  Capability Advertisement Selection . . . . . . . . . . . . . . 19
 8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   8.1.  VCCV Interface Parameters Sub-TLV  . . . . . . . . . . . . 19
     8.1.1.  MPLS VCCV Control Channel (CC) Types . . . . . . . . . 19
     8.1.2.  MPLS VCCV Connectivity Verification (CV) Types . . . . 20
   8.2.  PW Associated Channel Type . . . . . . . . . . . . . . . . 21
   8.3.  L2TPv3 Assignments . . . . . . . . . . . . . . . . . . . . 21
     8.3.1.  Control Message Attribute Value Pairs (AVPs) . . . . . 21
     8.3.2.  Default L2-Specific Sublayer Bits  . . . . . . . . . . 21
     8.3.3.  ATM-Specific Sublayer Bits . . . . . . . . . . . . . . 21
     8.3.4.  VCCV Capability AVP Values . . . . . . . . . . . . . . 22
 9.  Congestion Considerations  . . . . . . . . . . . . . . . . . . 23
 10. Security Considerations  . . . . . . . . . . . . . . . . . . . 24
 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
   12.1. Normative References . . . . . . . . . . . . . . . . . . . 26
   12.2. Informative References . . . . . . . . . . . . . . . . . . 26

Nadeau & Pignataro Standards Track [Page 2] RFC 5085 PW VCCV December 2007

1. Introduction

 There is a need for fault detection and diagnostic mechanisms that
 can be used for end-to-end fault detection and diagnostics for a
 Pseudowire, as a means of determining the PW's true operational
 state.  Operators have indicated in [RFC4377] and [RFC3916] that such
 a tool is required for PW operation and maintenance.  This document
 defines a protocol called Virtual Circuit Connectivity Verification
 (VCCV) that satisfies these requirements.  VCCV is, in its simplest
 description, a control channel between a pseudowire's ingress and
 egress points over which connectivity verification messages can be
 sent.
 The Pseudowire Edge-to-Edge Emulation (PWE3) Working Group defines a
 mechanism that emulates the essential attributes of a
 telecommunications service (such as a T1 leased line or Frame Relay)
 over a variety of Packet Switched Network (PSN) types [RFC3985].
 PWE3 is intended to provide only the minimum necessary functionality
 to emulate the service with the required degree of faithfulness for
 the given service definition.  The required functions of PWs include
 encapsulating service-specific bit streams, cells, or PDUs arriving
 at an ingress port and carrying them across an IP path or MPLS
 tunnel.  In some cases, it is necessary to perform other operations,
 such as managing their timing and order, to emulate the behavior and
 characteristics of the service to the required degree of
 faithfulness.
 From the perspective of Customer Edge (CE) devices, the PW is
 characterized as an unshared link or circuit of the chosen service.
 In some cases, there may be deficiencies in the PW emulation that
 impact the traffic carried over a PW and therefore limit the
 applicability of this technology.  These limitations must be fully
 described in the appropriate service-specific documentation.
 For each service type, there will be one default mode of operation
 that all PEs offering that service type must support.  However,
 optional modes have been defined to improve the faithfulness of the
 emulated service, as well as to offer a means by which older
 implementations may support these services.
 Figure 1 depicts the architecture of a pseudowire as defined in
 [RFC3985].  It further depicts where the VCCV control channel resides
 within this architecture, which will be discussed in detail shortly.

Nadeau & Pignataro Standards Track [Page 3] RFC 5085 PW VCCV December 2007

          |<-------------- Emulated Service ---------------->|
          |          |<---------- VCCV ---------->|          |
          |          |<------- Pseudowire ------->|          |
          |          |                            |          |
          |          |    |<-- PSN Tunnel -->|    |          |
          |          V    V                  V    V          |
          V    AC    +----+                  +----+     AC   V
    +-----+    |     | PE1|==================| PE2|     |    +-----+
    |     |----------|............PW1.............|----------|     |
    | CE1 |    |     |    |                  |    |     |    | CE2 |
    |     |----------|............PW2.............|----------|     |
    +-----+  ^ |     |    |==================|    |     | ^  +-----+
          ^  |       +----+                  +----+     | |  ^
          |  |   Provider Edge 1         Provider Edge 2  |  |
          |  |                                            |  |
    Customer |                                            | Customer
    Edge 1   |                                            | Edge 2
             |                                            |
             |                                            |
       Native service                               Native service
             Figure 1: PWE3 VCCV Operation Reference Model
 From Figure 1, Customer Edge (CE) routers CE1 and CE2 are attached to
 the emulated service via Attachment Circuits (ACs), and to each of
 the Provider Edge (PE) routers (PE1 and PE2, respectively).  An AC
 can be a Frame Relay Data Link Connection Identifier (DLCI), an ATM
 Virtual Path Identifier / Virtual Channel Identifier (VPI/VCI), an
 Ethernet port, etc.  The PE devices provide pseudowire emulation,
 enabling the CEs to communicate over the PSN.  A pseudowire exists
 between these PEs traversing the provider network.  VCCV provides
 several means of creating a control channel over the PW, between the
 PE routers that attach the PW.
 Figure 2 depicts how the VCCV control channel is associated with the
 pseudowire protocol stack.

Nadeau & Pignataro Standards Track [Page 4] RFC 5085 PW VCCV December 2007

     +-------------+                                +-------------+
     |  Layer2     |                                |  Layer2     |
     |  Emulated   |       < Emulated Service >     |  Emulated   |
     |  Services   |                                |  Services   |
     +-------------+                                +-------------+
     |             |            VCCV/PW             |             |
     |Demultiplexer|       < Control Channel >      |Demultiplexer|
     +-------------+                                +-------------+
     |    PSN      |          < PSN Tunnel >        |    PSN      |
     +-------------+                                +-------------+
     |  Physical   |                                |  Physical   |
     +-----+-------+                                +-----+-------+
           |                                              |
           |             ____     ___       ____          |
           |           _/    \___/   \    _/    \__       |
           |          /               \__/         \_     |
           |         /                               \    |
           +--------|      MPLS or IP Network         |---+
                     \                               /
                      \   ___      ___     __      _/
                       \_/   \____/   \___/  \____/
   Figure 2: PWE3 Protocol Stack Reference Model including the VCCV
                            Control Channel
 VCCV messages are encapsulated using the PWE3 encapsulation as
 described in Sections 5 and 6, so that they are handled and processed
 in the same manner (or in some cases, a similar manner) as the PW
 PDUs for which they provide a control channel.  These VCCV messages
 are exchanged only after the capability (expressed as two VCCV type
 spaces, namely the VCCV Control Channel and Connectivity Verification
 Types) and desire to exchange such traffic has been advertised
 between the PEs (see Sections 5.3 and 6.3), and VCCV types chosen.

1.1. Specification of Requirements

 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 [RFC2119].

2. Abbreviations

 AC      Attachment Circuit [RFC3985].
 AVP     Attribute Value Pair [RFC3931].
 CC      Control Channel (used as CC Type).

Nadeau & Pignataro Standards Track [Page 5] RFC 5085 PW VCCV December 2007

 CE      Customer Edge.
 CV      Connectivity Verification (used as CV Type).
 CW      Control Word [RFC3985].
 L2SS    L2-Specific Sublayer [RFC3931].
 LCCE    L2TP Control Connection Endpoint [RFC3931].
 OAM     Operation and Maintenance.
 PE      Provider Edge.
 PSN     Packet Switched Network [RFC3985].
 PW      Pseudowire [RFC3985].
 PW-ACH  PW Associated Channel Header [RFC4385].
 VCCV    Virtual Circuit Connectivity Verification.

3. Overview of VCCV

 The goal of VCCV is to verify and further diagnose the pseudowire
 forwarding path.  To this end, VCCV is comprised of different
 components:
 o  a means of signaling VCCV capabilities to a peer PE,
 o  an encapsulation for the VCCV control channel messages that allows
    the receiving PE to intercept, interpret, and process them locally
    as OAM messages, and
 o  specifications for the operation of the various VCCV operational
    modes transmitted within the VCCV messages.
 When a pseudowire is first signaled using the Label Distribution
 Protocol (LDP) [RFC4447] or the Layer Two Tunneling Protocol version
 3 (L2TPv3) [RFC3931], a message is sent from the initiating PE to the
 receiving PE requesting that a pseudowire be set up.  This message
 has been extended to include VCCV capability information (see
 Section 4).  The VCCV capability information indicates to the
 receiving PE which combinations of Control Channel (CC) and
 Connectivity Verification (CV) Types it is capable of receiving.  If
 the receiving PE agrees to establish the PW, it will return its
 capabilities in the subsequent signaling message to indicate which CC

Nadeau & Pignataro Standards Track [Page 6] RFC 5085 PW VCCV December 2007

 and CV Types it is capable of processing.  Precedence rules for which
 CC and CV Type to choose in cases where more than one is specified in
 this message are defined in Section 7 of this document.
 Once the PW is signaled, data for the PW will flow between the PEs
 terminating the PW.  At this time, the PEs can begin transmitting
 VCCV messages based on the CC and CV Type combinations just
 discussed.  To this end, VCCV defines an encapsulation for these
 messages that identifies them as belonging to the control channel for
 the PW.  This encapsulation is designed to both allow the control
 channel to be processed functionally in the same manner as the data
 traffic for the PW in order to faithfully test the data plane for the
 PE, and allow the PE to intercept and process these VCCV messages
 instead of forwarding them out of the AC towards the CE as if they
 were data traffic.  In this way, the most basic function of the VCCV
 control channel is to verify connectivity of the pseudowire and the
 data plane used to transport the data path for the pseudowire.  It
 should be noted that because of the number of combinations of
 optional and mandatory data-plane encapsulations for PW data traffic,
 VCCV defines a number of Control Channel (CC) and Connectivity
 Verification (CV) types in order to support as many of these as
 possible.  While designed to support most of the existing
 combinations (both mandatory and optional), VCCV does define a
 default CC and CV Type combination for each PW Demultiplexer type, as
 will be described in detail later in this document.
 VCCV can be used both as a fault detection and/or a diagnostic tool
 for pseudowires.  For example, an operator can periodically invoke
 VCCV on a timed, on-going basis for proactive connectivity
 verification on an active pseudowire, or on an ad hoc or as-needed
 basis as a means of manual connectivity verification.  When invoking
 VCCV, the operator triggers a combination of one of its various CC
 Types and one of its various CV Types.  The CV Types include LSP Ping
 [RFC4379] for MPLS PWs, and ICMP Ping [RFC0792] [RFC4443] for both
 MPLS and L2TPv3 PWs.  We define a matrix of acceptable CC and CV Type
 combinations further in this specification.
 The control channel maintained by VCCV can additionally carry fault
 detection status between the endpoints of the pseudowire.
 Furthermore, this information can then be translated into the native
 OAM status codes used by the native access technologies, such as ATM,
 Frame-Relay or Ethernet.  The specific details of such status
 interworking is out of the scope of this document, and is only noted
 here to illustrate the utility of VCCV for such purposes.  Complete
 details can be found in [MSG-MAP] and [RFC4447].

Nadeau & Pignataro Standards Track [Page 7] RFC 5085 PW VCCV December 2007

4. CC Types and CV Types

 The VCCV Control Channel (CC) Type defines several possible types of
 control channel that VCCV can support.  These control channels can in
 turn carry several types of protocols defined by the Connectivity
 Verification (CV) Type.  VCCV potentially supports multiple CV Types
 concurrently, but it only supports the use of a single CC Type.  The
 specific type or types of VCCV packets that can be accepted and sent
 by a router are indicated during capability advertisement as
 described in Sections 5.3 and 6.3.  The various VCCV CV Types
 supported are used only when they apply to the context of the PW
 demultiplexer in use.  For example, the LSP Ping CV Type should only
 be used when MPLS Labels are utilized as PW Demultiplexer.
 Once a set of VCCV capabilities is received and advertised, a CC Type
 and CV Type(s) that match both the received and transmitted
 capabilities can be selected.  That is, a PE router needs to only
 allow Types that are both received and advertised to be selected,
 performing a logical AND between the received and transmitted bitflag
 fields.  The specific CC Type and CV Type(s) are then chosen within
 the constraints and rules specified in Section 7.  Once a specific CC
 Type has been chosen (i.e., it matches both the transmitted and
 received VCCV CC capability), transmitted and replied to, this CC
 Type MUST be the only one used until such time as the pseudowire is
 re-signaled.  In addition, based on these rules and the procedures
 defined in Section 5.2 of [RFC4447], the pseudowire MUST be re-
 signaled if a different set of capabilities types is desired.  The
 relevant portion of Section 5.2 of [RFC4447] is:
       Interface Parameter Sub-TLV
       Note that as the "interface parameter sub-TLV" is part of the
       FEC, the rules of LDP make it impossible to change the
       interface parameters once the pseudowire has been set up.
 The CC and CV Type indicator fields are defined as 8-bit bitmasks
 used to indicate the specific CC or CV Type or Types (i.e., none,
 one, or more) of control channel packets that may be sent on the VCCV
 control channel.  These values represent the numerical value
 corresponding to the actual bit being set in the bitfield.  The
 definition of each CC and CV Type is dependent on the PW type
 context, either MPLS or L2TPv3, within which it is defined.

Nadeau & Pignataro Standards Track [Page 8] RFC 5085 PW VCCV December 2007

 Control Channel (CC) Types:
    The defined values for CC Types for MPLS PWs are:
       MPLS Control Channel (CC) Types:
       Bit (Value)    Description
       ============   ==========================================
       Bit 0 (0x01) - Type 1: PWE3 Control Word with 0001b as
                      first nibble (PW-ACH, see [RFC4385])
       Bit 1 (0x02) - Type 2: MPLS Router Alert Label
       Bit 2 (0x04) - Type 3: MPLS PW Label with TTL == 1
       Bit 3 (0x08) - Reserved
       Bit 4 (0x10) - Reserved
       Bit 5 (0x20) - Reserved
       Bit 6 (0x40) - Reserved
       Bit 7 (0x80) - Reserved
    The defined values for CC Types for L2TPv3 PWs are:
       L2TPv3 Control Channel (CC) Types:
       Bit (Value)    Description
       ============   ==========================================
       Bit 0 (0x01) - L2-Specific Sublayer with V-bit set
       Bit 1 (0x02) - Reserved
       Bit 2 (0x04) - Reserved
       Bit 3 (0x08) - Reserved
       Bit 4 (0x10) - Reserved
       Bit 5 (0x20) - Reserved
       Bit 6 (0x40) - Reserved
       Bit 7 (0x80) - Reserved
 Connectivity Verification (CV) Types:
    The defined values for CV Types for MPLS PWs are:
       MPLS Connectivity Verification (CV) Types:
       Bit (Value)    Description
       ============   ==========================================
       Bit 0 (0x01) - ICMP Ping
       Bit 1 (0x02) - LSP Ping
       Bit 2 (0x04) - Reserved
       Bit 3 (0x08) - Reserved
       Bit 4 (0x10) - Reserved
       Bit 5 (0x20) - Reserved

Nadeau & Pignataro Standards Track [Page 9] RFC 5085 PW VCCV December 2007

       Bit 6 (0x40) - Reserved
       Bit 7 (0x80) - Reserved
    The defined values for CV Types for L2TPv3 PWs are:
       L2TPv3 Connectivity Verification (CV) Types:
       Bit (Value)    Description
       ============   ==========================================
       Bit 0 (0x01) - ICMP Ping
       Bit 1 (0x02) - Reserved
       Bit 2 (0x04) - Reserved
       Bit 3 (0x08) - Reserved
       Bit 4 (0x10) - Reserved
       Bit 5 (0x20) - Reserved
       Bit 6 (0x40) - Reserved
       Bit 7 (0x80) - Reserved
 If none of the types above are supported, the entire CC and CV Type
 Indicator fields SHOULD be transmitted as 0x00 (i.e., all bits in the
 bitfield set to 0) to indicate this to the peer.
 If no capability is signaled, then the peer MUST assume that the peer
 has no VCCV capability and follow the procedures specified in this
 document for this case.

5. VCCV Control Channel for MPLS PWs

 When MPLS is used to transport PW packets, VCCV packets are carried
 over the MPLS LSP as defined in this section.  In order to apply IP
 monitoring tools to a PW, an operator may configure VCCV as a control
 channel for the PW between the PE's endpoints [RFC3985].  Packets
 sent across this channel from the source PE towards the destination
 PE either as in-band traffic with the PW's data, or out-of-band.  In
 all cases, the control channel traffic is not forwarded past the PE
 endpoints towards the Customer Edge (CE) devices; instead, VCCV
 messages are intercepted at the PE endpoints for exception
 processing.

5.1. VCCV Control Channel Types for MPLS

 As already described in Section 4, the capability of which control
 channel types (CC Type) are supported is advertised by a PE.  Once
 the receiving PE has chosen a CC Type mode to use, it MUST continue
 using this mode until such time as the PW is re-signaled.  Thus, if a
 new CC Type is desired, the PW must be torn-down and re-established.

Nadeau & Pignataro Standards Track [Page 10] RFC 5085 PW VCCV December 2007

 Ideally, such a control channel would be completely in-band (i.e.,
 following the same data-plane faith as PW data).  When a control word
 is present on the PW, it is possible to indicate the control channel
 by setting a bit in the control word header (see Section 5.1.1).
 Section 5.1.1 through Section 5.1.3 describe each of the currently
 defined VCCV Control Channel Types (CC Types).

5.1.1. In-Band VCCV (Type 1)

 CC Type 1 is also referred to as "PWE3 Control Word with 0001b as
 first nibble".  It uses the PW Associated Channel Header (PW-ACH);
 see Section 5 of [RFC4385].
 The PW set-up protocol [RFC4447] determines whether a PW uses a
 control word.  When a control word is used, and that CW uses the
 "Generic PW MPLS Control Word" format (see Section 3 of [RFC4385]), a
 Control Channel for use of VCCV messages can be created by using the
 PW Associated Channel CW format (see Section 5 of [RFC4385]).
 The PW Associated Channel for VCCV control channel traffic is defined
 in [RFC4385] as shown in Figure 3:
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0 0 0 1|Version|   Reserved    |         Channel Type          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 3: PW Associated Channel Header
 The first nibble is set to 0001b to indicate a channel associated
 with a pseudowire (see Section 5 of [RFC4385] and Section 3.6 of
 [RFC4446]).  The Version and the Reserved fields are set to 0, and
 the Channel Type is set to 0x0021 for IPv4 and 0x0057 for IPv6
 payloads.
 For example, Figure 4 shows how the Ethernet [RFC4448] PW-ACH would
 be received containing an LSP Ping payload corresponding to a choice
 of CC Type of 0x01 and a CV Type of 0x02:
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0|   0x21 (IPv4) or 0x57 (IPv6)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            Figure 4: PW Associated Channel Header for VCCV

Nadeau & Pignataro Standards Track [Page 11] RFC 5085 PW VCCV December 2007

 It should be noted that although some PW types are not required to
 carry the control word, this type of VCCV can only be used for those
 PW types that do employ the control word when it is in use.  Further,
 this CC Type can only be used if the PW CW follows the "Generic PW
 MPLS Control Word" format.  This mode of VCCV operation MUST be
 supported when the control word is present.

5.1.2. Out-of-Band VCCV (Type 2)

 CC Type 2 is also referred to as "MPLS Router Alert Label".
 A VCCV control channel can alternatively be created by using the MPLS
 router alert label [RFC3032] immediately above the PW label.  It
 should be noted that this approach could result in a different Equal
 Cost Multi-Path (ECMP) hashing behavior than pseudowire PDUs, and
 thus result in the VCCV control channel traffic taking a path which
 differs from that of the actual data traffic under test.  Please see
 Section 2 of [RFC4928].
 CC Type 2 can be used whether the PW is set-up with a Control Word
 present or not.
 This is the preferred mode of VCCV operation when the Control Word is
 not present.
 If the Control Word is in use on this PW, it MUST also be included
 before the VCCV message.  This is done to avoid the different ECMP
 hashing behavior.  In this case, the CW uses the PW-ACH format
 described in Section 5.1.1 (see Figures 3 and 4).  If the Control
 Word is not in use on this PW, the VCCV message follows the PW Label
 directly.

5.1.3. TTL Expiry VCCV (Type 3)

 CC Type 3 is also referred to as "MPLS PW Label with TTL == 1".
 The TTL of the PW label can be set to 1 to force the packet to be
 processed within the destination router's control plane.  This
 approach could also result in a different ECMP hashing behavior and
 VCCV messages taking a different path than the PW data traffic.
 CC Type 3 can be used whether the PW is set-up with a Control Word
 present or not.
 If the Control Word is in use on this PW, it MUST also be included
 before the VCCV message.  This is done to avoid the different ECMP
 hashing behavior.  In this case, the CW uses the PW-ACH format

Nadeau & Pignataro Standards Track [Page 12] RFC 5085 PW VCCV December 2007

 described in Section 5.1.1 (see Figures 3 and 4).  If the Control
 Word is not in use on this PW, the VCCV message follows the PW Label
 directly.

5.2. VCCV Connectivity Verification Types for MPLS

5.2.1. ICMP Ping

 When this optional connectivity verification mode is used, an ICMP
 Echo packet using the encoding specified in [RFC0792] (ICMPv4) or
 [RFC4443] (ICMPv6) achieves connectivity verification.
 Implementations MUST use ICMPv4 [RFC0792] if the signaling for VCCV
 used IPv4 addresses, or ICMPv6 [RFC4443] if IPv6 addresses were used.
 If the pseudowire is set up statically, then the encoding MUST use
 that which was used for the pseudowire in the configuration.

5.2.2. MPLS LSP Ping

 The LSP Ping header MUST be used in accordance with [RFC4379] and
 MUST also contain the target FEC Stack containing the sub-TLV of sub-
 Type 8 for the "L2 VPN endpoint", 9 for "FEC 128 Pseudowire
 (deprecated)", 10 for "FEC 128 Pseudowire", or 11 for the "FEC 129
 Pseudowire".  The sub-TLV value indicates the PW to be verified.

5.3. VCCV Capability Advertisement for MPLS PWs

 To permit the indication of the type or types of PW control
 channel(s) and connectivity verification mode or modes over a
 particular PW, a VCCV parameter is defined in Section 5.3.1 that is
 used as part of the PW establishment signaling.  When a PE signals a
 PW and desires PW OAM for that PW, it MUST indicate this during PW
 establishment using the messages defined in Section 5.3.1.
 Specifically, the PE MUST include the VCCV interface parameter sub-
 TLV (0x0C) assigned in [RFC4446] in the PW set-up message [RFC4447].
 The decision of the type of VCCV control channel is left completely
 to the receiving control entity, although the set of choices is given
 by the sender in that it indicates the control channels and
 connectivity verification type or types that it can understand.  The
 receiver SHOULD choose a single Control Channel Type from the match
 between the choices sent and received, based on the capability
 advertisement selection specified in Section 7, and it MUST continue
 to use this type for the duration of the life of the control channel.
 Changing Control Channel Types after one has been established to be
 in use could potentially cause problems at the receiving end and
 could also lead to interoperability issues; thus, it is NOT
 RECOMMENDED.

Nadeau & Pignataro Standards Track [Page 13] RFC 5085 PW VCCV December 2007

 When a PE sends a label mapping message for a PW, it uses the VCCV
 parameter to indicate the type of OAM control channels and
 connectivity verification type or types it is willing to receive and
 can send on that PW.  A remote PE MUST NOT send VCCV messages before
 the capability of supporting the control channel(s) (and connectivity
 verification type(s) to be used over them) is signaled.  Then, it can
 do so only on a control channel and using the connectivity
 verification type(s) from the ones indicated.
 If a PE receives VCCV messages prior to advertising capability for
 this message, it MUST discard these messages and not reply to them.
 In this case, the PE SHOULD increment an error counter and optionally
 issue a system and/or SNMP notification to indicate to the system
 administrator that this condition exists.
 When LDP is used as the PW signaling protocol, the requesting PE
 indicates its configured VCCV capability or capabilities to the
 remote PE by including the VCCV parameter with appropriate options in
 the VCCV interface parameter sub-TLV field of the PW ID FEC TLV (FEC
 128) or in the interface parameter sub-TLV of the Generalized PW ID
 FEC TLV (FEC 129).  These options indicate which control channel and
 connectivity verification types it supports.  The requesting PE MAY
 indicate that it supports multiple control channel options, and in
 doing so, it agrees to support any and all indicated types if
 transmitted to it.  However, it MUST do so in accordance with the
 rules stipulated in Section 5.3.1 (VCCV Capability Advertisement Sub-
 TLV.)
 Local policy may direct the PE to support certain OAM capability and
 to indicate it.  The absence of the VCCV parameter indicates that no
 OAM functions are supported by the requesting PE, and thus the
 receiving PE MUST NOT send any VCCV control channel traffic to it.
 The reception of a VCCV parameter with no options set MUST be ignored
 as if one is not transmitted at all.
 The receiving PE similarly indicates its supported control channel
 types in the label mapping message.  These may or may not be the same
 as the ones that were sent to it.  The sender should examine the set
 that is returned to understand which control channels it may
 establish with the remote peer, as specified in Sections 4 and 7.
 Similarly, it MUST NOT send control channel traffic to the remote PE
 for which the remote PE has not indicated it supports.

5.3.1. VCCV Capability Advertisement LDP Sub-TLV

 [RFC4447] defines an Interface Parameter Sub-TLV field in the LDP PW
 ID FEC (FEC 128) and an Interface Parameters TLV in the LDP
 Generalized PW ID FEC (FEC 129) to signal different capabilities for

Nadeau & Pignataro Standards Track [Page 14] RFC 5085 PW VCCV December 2007

 specific PWs.  An optional sub-TLV parameter is defined to indicate
 the capability of supporting none, one, or more control channel and
 connectivity verification types for VCCV.  This is the VCCV parameter
 field.  If FEC 128 is used, the VCCV parameter field is carried in
 the Interface Parameter sub-TLV field.  If FEC 129 is used, it is
 carried as an Interface Parameter sub-TLV in the Interface Parameters
 TLV.
 The VCCV parameter ID is defined as follows in [RFC4446]:
 Parameter ID   Length     Description
   0x0c           4           VCCV
 The format of the VCCV parameter field is as follows:
  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |      0x0c     |       0x04    |   CC Types    |   CV Types    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The Control Channel Type field (CC Type) defines a bitmask used to
 indicate the type of control channel(s) (i.e., none, one, or more)
 that a router is capable of receiving control channel traffic on.  If
 more than one control channel is specified, the router agrees to
 accept control traffic over either control channel; however, see the
 rules specified in Sections 4 and 7 for more details.  If none of the
 types are supported, a CC Type Indicator of 0x00 SHOULD be
 transmitted to indicate this to the peer.  However, if no capability
 is signaled, then the PE MUST assume that its peer is incapable of
 receiving any of the VCCV CC Types and MUST NOT send any OAM control
 channel traffic to it.  Note that the CC and CV Types definitions are
 consistent regardless of the PW's transport or access circuit type.
 The CC and CV Type values are defined in Section 4.

6. VCCV Control Channel for L2TPv3/IP PWs

 When L2TPv3 is used to set up a PW over an IP PSN, VCCV packets are
 carried over the L2TPv3 session as defined in this section.  L2TPv3
 provides a "Hello" keepalive mechanism for the L2TPv3 control plane
 that operates in-band over IP or UDP (see Section 4.4 of [RFC3931]).
 This built-in Hello facility provides dead peer and path detection
 only for the group of sessions associated with the L2TP Control
 Connection.  VCCV, however, allows individual L2TP sessions to be
 tested.  This provides a more granular mechanism which can be used to
 troubleshoot potential problems within the data plane of L2TP
 endpoints themselves, or to provide additional connection status of
 individual pseudowires.

Nadeau & Pignataro Standards Track [Page 15] RFC 5085 PW VCCV December 2007

 The capability of which Control Channel Type (CC Type) to use is
 advertised by a PE to indicate which of the potentially various
 control channel types are supported.  Once the receiving PE has
 chosen a mode to use, it MUST continue using this mode until such
 time as the PW is re-signaled.  Thus, if a new CC Type is desired,
 the PW must be torn down and re-established.
 An LCCE sends VCCV messages on an L2TPv3-signaled pseudowire for
 fault detection and diagnostic of the L2TPv3 session.  The VCCV
 message travels in-band with the Session and follows the exact same
 path as the user data for the session, because the IP header and
 L2TPv3 Session header are identical.  The egress LCCE of the L2TPv3
 session intercepts and processes the VCCV message, and verifies the
 signaling and forwarding state of the pseudowire on reception of the
 VCCV message.  It is to be noted that the VCCV mechanism for L2TPv3
 is primarily targeted at verifying the pseudowire forwarding and
 signaling state at the egress LCCE.  It also helps when L2TPv3
 Control Connection and Session paths are not identical.

6.1. VCCV Control Channel Type for L2TPv3

 In order to carry VCCV messages within an L2TPv3 session data packet,
 the PW MUST be established such that an L2-Specific Sublayer (L2SS)
 that defines the V-bit is present.  This document defines the V-bit
 for the Default L2-Specific Sublayer [RFC3931] and the ATM-Specific
 Sublayer [RFC4454] using the Bit 0 position (see Sections 8.3.2 and
 8.3.3).  The L2-Specific Sublayer presence and type (either the
 Default or a PW-Specific L2SS) is signaled via the L2-Specific
 Sublayer AVP, Attribute Type 69, as defined in [RFC3931].  The V-bit
 within the L2-Specific Sublayer is used to identify that a VCCV
 message follows, and when the V-bit is set the L2SS has the format
 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|0 0 0|Version|   Reserved    |         Channel Type          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  Figure 5: L2-Specific Sublayer Format when the V-bit (bit 0) is set
 The VCCV messages are distinguished from user data by the V-bit.  The
 V-bit is set to 1, indicating that a VCCV session message follows.
 The next three bits MUST be set to 0 when sending and ignored upon
 receipt.  The remaining fields comprising 28 bits (i.e., Version,
 Reserved, and Channel Type) follow the same definition, format, and
 number registry from Section 5 of [RFC4385].

Nadeau & Pignataro Standards Track [Page 16] RFC 5085 PW VCCV December 2007

 The Version and Reserved fields are set to 0.  For the CV Type
 currently defined of ICMP Ping (0x01), the Channel Type can indicate
 IPv4 (0x0021) or IPv6 (0x0057) (see [RFC4385]) as the VCCV payload
 directly following the L2SS.

6.2. VCCV Connectivity Verification Type for L2TPv3

 The VCCV message over L2TPv3 directly follows the L2-Specific
 Sublayer with the V-bit set.  It MUST contain an ICMP Echo packet as
 described in Section 6.2.1.

6.2.1. L2TPv3 VCCV using ICMP Ping

 When this connectivity verification mode is used, an ICMP Echo packet
 using the encoding specified in [RFC0792] for (ICMPv4) or [RFC4443]
 (for ICMPv6) achieves connectivity verification.  Implementations
 MUST use ICMPv4 [RFC0792] if the signaling for the L2TPv3 PW used
 IPv4 addresses, or ICMPv6 [RFC4443] if IPv6 addresses were used.  If
 the pseudowire is set-up statically, then the encoding MUST use that
 which was used for the pseudowire in the configuration.
 The ICMP Ping packet directly follows the L2SS with the V-bit set.
 In the ICMP Echo request, the IP Header fields MUST have the
 following values: the destination IP address is set to the remote
 LCCE's IP address for the tunnel endpoint, the source IP address is
 set to the local LCCE's IP address for the tunnel endpoint, and the
 TTL or Hop Limit is set to 1.

6.3. L2TPv3 VCCV Capability Advertisement for L2TPv3

 A new optional AVP is defined in Section 6.3.1 to indicate the VCCV
 capabilities during session establishment.  An LCCE MUST signal its
 desire to use connectivity verification for a particular L2TPv3
 session and its VCCV capabilities using the VCCV Capability AVP.
 An LCCE MUST NOT send VCCV packets on an L2TPv3 session unless it has
 received VCCV capability by means of the VCCV Capability AVP from the
 remote end.  If an LCCE receives VCCV packets and it is not VCCV
 capable or it has not sent VCCV capability indication to the remote
 end, it MUST discard these messages.  It should also increment an
 error counter.  In this case the LCCE MAY optionally issue a system
 and/or SNMP notification.

6.3.1. L2TPv3 VCCV Capability AVP

 The "VCCV Capability AVP", Attribute Type 96, specifies the VCCV
 capabilities as a pair of bitflags for the Control Channel (CC) and
 Connectivity Verification (CV) Types.  This AVP is exchanged during

Nadeau & Pignataro Standards Track [Page 17] RFC 5085 PW VCCV December 2007

 session establishment (in ICRQ (Incoming-Call-Request), ICRP
 (Incoming-Call-Reply), OCRQ (Outgoing-Call-Request), or OCRP
 (Outgoing-Call-Reply) messages).  The value field has the following
 format:
 VCCV Capability AVP (ICRQ, ICRP, OCRQ, OCRP)
     0                   1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   CC Types    |   CV Types    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 CC Types:
    The Control Channel (CC) Types field defines a bitmask used to
    indicate the type of control channel(s) that may be used to
    receive OAM traffic on for the given Session.  The router agrees
    to accept VCCV traffic at any time over any of the signaled VCCV
    control channel types.  CC Type values are defined in Section 4.
    Although there is only one value defined in this document, the CC
    Types field is included for forward compatibility should further
    CC Types need to be defined in the future.
    A CC Type of 0x01 may only be requested when there is an L2-
    Specific Sublayer that defines the V-bit present.  If a CC Type of
    0x01 is requested without requesting an L2-Specific Sublayer AVP
    with an L2SS type that defines the V-bit, the session MUST be
    disconnected with a Call-Disconnect-Notify (CDN) message.
    If no CC Type is supported, a CC Type Indicator of 0x00 SHOULD be
    sent.
 CV Types:
    The Connectivity Verification (CV) Types field defines a bitmask
    used to indicate the specific type or types (i.e., none, one, or
    more) of control packets that may be sent on the specified VCCV
    control channel.  CV Type values are defined in Section 4.
 If no VCCV Capability AVP is signaled, then the LCCE MUST assume that
 the peer is incapable of receiving VCCV and MUST NOT send any OAM
 control channel traffic to it.

Nadeau & Pignataro Standards Track [Page 18] RFC 5085 PW VCCV December 2007

 All L2TP AVPs have an M (Mandatory) bit, H (Hidden) bit, Length, and
 Vendor ID.  The Vendor ID for the VCCV Capability AVP MUST be 0,
 indicating that this is an IETF-defined AVP.  This AVP MAY be hidden
 (the H bit MAY be 0 or 1).  The M bit for this AVP SHOULD be set to
 0.  The Length (before hiding) of this AVP is 8.

7. Capability Advertisement Selection

 When a PE receives a VCCV capability advertisement, the advertisement
 may potentially contain more than one CC or CV Type.  Only matching
 capabilities can be selected.  When multiple capabilities match, only
 one CC Type MUST be used.
 In particular, as already specified, once a valid CC Type is used by
 a PE (traffic sent using that encapsulation), the PE MUST NOT send
 any traffic down another CC Type control channel.
 For cases where multiple CC Types are advertised, the following
 precedence rules apply when choosing the single CC Type to use:
 1.  Type 1: PWE3 Control Word with 0001b as first nibble
 2.  Type 2: MPLS Router Alert Label
 3.  Type 3: MPLS PW Label with TTL == 1
 For MPLS PWs, the CV Type of LSP Ping (0x02) is the default, and the
 CV Type of ICMP Ping (0x01) is optional.

8. IANA Considerations

8.1. VCCV Interface Parameters Sub-TLV

 The VCCV Interface Parameters Sub-TLV codepoint is defined in
 [RFC4446].  IANA has created and will maintain registries for the CC
 Types and CV Types (bitmasks in the VCCV Parameter ID).  The CC Type
 and CV Type new registries (see Sections 8.1.1 and 8.1.2,
 respectively) have been created in the Pseudo Wires Name Spaces,
 reachable from [IANA.pwe3-parameters].  The allocations must be done
 using the "IETF Consensus" policy defined in [RFC2434].

8.1.1. MPLS VCCV Control Channel (CC) Types

 IANA has set up a registry of "MPLS VCCV Control Channel Types".
 These are 8 bitfields.  CC Type values 0x01, 0x02, and 0x04 are
 specified in Section 4 of this document.  The remaining bitfield
 values (0x08, 0x10, 0x20, 0x40, and 0x80) are to be assigned by IANA
 using the "IETF Consensus" policy defined in [RFC2434].  A VCCV

Nadeau & Pignataro Standards Track [Page 19] RFC 5085 PW VCCV December 2007

 Control Channel Type description and a reference to an RFC approved
 by the IESG are required for any assignment from this registry.
    MPLS Control Channel (CC) Types:
    Bit (Value)    Description
    ============   ==========================================
    Bit 0 (0x01) - Type 1: PWE3 Control Word with 0001b as
                   first nibble (PW-ACH, see [RFC4385])
    Bit 1 (0x02) - Type 2: MPLS Router Alert Label
    Bit 2 (0x04) - Type 3: MPLS PW Label with TTL == 1
    Bit 3 (0x08) - Reserved
    Bit 4 (0x10) - Reserved
    Bit 5 (0x20) - Reserved
    Bit 6 (0x40) - Reserved
    Bit 7 (0x80) - Reserved
 The most significant (high order) bit is labeled Bit 7, and the least
 significant (low order) bit is labeled Bit 0, see parenthetical
 "Value".

8.1.2. MPLS VCCV Connectivity Verification (CV) Types

 IANA has set up a registry of "MPLS VCCV Control Verification Types".
 These are 8 bitfields.  CV Type values 0x01 and 0x02 are specified in
 Section 4 of this document.  The remaining bitfield values (0x04,
 0x08, 0x10, 0x20, 0x40, and 0x80) are to be assigned by IANA using
 the "IETF Consensus" policy defined in [RFC2434].  A VCCV Control
 Verification Type description and a reference to an RFC approved by
 the IESG are required for any assignment from this registry.
    MPLS Connectivity Verification (CV) Types:
    Bit (Value)    Description
    ============   ==========================================
    Bit 0 (0x01) - ICMP Ping
    Bit 1 (0x02) - LSP Ping
    Bit 2 (0x04) - Reserved
    Bit 3 (0x08) - Reserved
    Bit 4 (0x10) - Reserved
    Bit 5 (0x20) - Reserved
    Bit 6 (0x40) - Reserved
    Bit 7 (0x80) - Reserved
 The most significant (high order) bit is labeled Bit 7, and the least
 significant (low order) bit is labeled Bit 0, see parenthetical
 "Value".

Nadeau & Pignataro Standards Track [Page 20] RFC 5085 PW VCCV December 2007

8.2. PW Associated Channel Type

 The PW Associated Channel Types used by VCCV as defined in Sections
 5.1.1 and 6.1 rely on previously allocated numbers from the
 Pseudowire Associated Channel Types Registry [RFC4385] in the Pseudo
 Wires Name Spaces reachable from [IANA.pwe3-parameters].  In
 particular, 0x21 (Internet Protocol version 4) MUST be used whenever
 an IPv4 payload follows the Pseudowire Associated Channel Header, or
 0x57 MUST be used when an IPv6 payload follows the Pseudowire
 Associated Channel Header.

8.3. L2TPv3 Assignments

 Section 8.3.1 through Section 8.3.3 are registrations of new L2TP
 values for registries already managed by IANA.  Section 8.3.4 is a
 new registry that has been added to the existing L2TP name spaces,
 and will be maintained by IANA accordingly.  The Layer Two Tunneling
 Protocol "L2TP" Name Spaces are reachable from
 [IANA.l2tp-parameters].

8.3.1. Control Message Attribute Value Pairs (AVPs)

 An additional AVP Attribute is specified in Section 6.3.1.  It was
 defined by IANA as described in Section 2.2 of [RFC3438].
    Attribute
    Type        Description
    ---------   ----------------------------------
    96          VCCV Capability AVP

8.3.2. Default L2-Specific Sublayer Bits

 The Default L2-Specific Sublayer contains 8 bits in the low-order
 portion of the header.  This document defines one reserved bit in the
 Default L2-Specific Sublayer in Section 6.1, which was assigned by
 IANA following IETF Consensus [RFC2434].
    Default L2-Specific Sublayer bits - per [RFC3931]
    ---------------------------------
    Bit 0 - V (VCCV) bit

8.3.3. ATM-Specific Sublayer Bits

 The ATM-Specific Sublayer contains 8 bits in the low-order portion of
 the header.  This document defines one reserved bit in the ATM-
 Specific Sublayer in Section 6.1, which was assigned by IANA
 following IETF Consensus [RFC2434].

Nadeau & Pignataro Standards Track [Page 21] RFC 5085 PW VCCV December 2007

    ATM-Specific Sublayer bits - per [RFC4454]
    --------------------------
    Bit 0 - V (VCCV) bit

8.3.4. VCCV Capability AVP Values

 This is a new registry that IANA maintains in the L2TP Name Spaces.
 IANA created and maintains a registry for the CC Types and CV Types
 bitmasks in the VCCV Capability AVP, defined in Section 6.3.1.  The
 allocations must be done using the "IETF Consensus" policy defined in
 [RFC2434].  A VCCV CC or CV Type description and a reference to an
 RFC approved by the IESG are required for any assignment from this
 registry.
 IANA has reserved the following bits in this registry:
    VCCV Capability AVP (Attribute Type 96) Values
    ---------------------------------------------------
    L2TPv3 Control Channel (CC) Types:
       Bit (Value)    Description
       ============   ==========================================
       Bit 0 (0x01) - L2-Specific Sublayer with V-bit set
       Bit 1 (0x02) - Reserved
       Bit 2 (0x04) - Reserved
       Bit 3 (0x08) - Reserved
       Bit 4 (0x10) - Reserved
       Bit 5 (0x20) - Reserved
       Bit 6 (0x40) - Reserved
       Bit 7 (0x80) - Reserved
    L2TPv3 Connectivity Verification (CV) Types:
       Bit (Value)    Description
       ============   ==========================================
       Bit 0 (0x01) - ICMP Ping
       Bit 1 (0x02) - Reserved
       Bit 2 (0x04) - Reserved
       Bit 3 (0x08) - Reserved
       Bit 4 (0x10) - Reserved
       Bit 5 (0x20) - Reserved
       Bit 6 (0x40) - Reserved
       Bit 7 (0x80) - Reserved

Nadeau & Pignataro Standards Track [Page 22] RFC 5085 PW VCCV December 2007

 The most significant (high order) bit is labeled Bit 7, and the least
 significant (low order) bit is labeled Bit 0, see parenthetical
 "Value".

9. Congestion Considerations

 The bandwidth resources used by VCCV are recommended to be minimal
 compared to those of the associated PW.  The bandwidth required for
 the VCCV channel is taken outside any allocation for PW data traffic,
 and can be configurable.  When doing resource reservation or network
 planning, the bandwidth requirements for both PW data and VCCV
 traffic need to be taken into account.
 VCCV applications (i.e., Connectivity Verification (CV) Types) MUST
 consider congestion and bandwidth usage implications and provide
 details on bandwidth or packet frequency management.  VCCV
 applications can have built-in bandwidth management in their
 protocols.  Other VCCV applications can have their bandwidth
 configuration-limited, and rate-limiting them can be harmful as it
 could translate to incorrectly declaring connectivity failures.  For
 all other VCCV applications, outgoing VCCV messages SHOULD be rate-
 limited to prevent aggressive connectivity verification consuming
 excessive bandwidth, causing congestion, becoming denial-of-service
 attacks, or generating an excessive packet rate at the CE-bound PE.
 If these conditions cannot be followed, an adaptive loss-based scheme
 SHOULD be applied to congestion-control outgoing VCCV traffic, so
 that it competes fairly with TCP within an order of magnitude.  One
 method of determining an acceptable bandwidth for VCCV is described
 in [RFC3448] (TFRC); other methods exist.  For example, bandwidth or
 packet frequency management can include any of the following: a
 negotiation of transmission interval/rate, a throttled transmission
 rate on "congestion detected" situations, a slow-start after shutdown
 due to congestion and until basic connectivity is verified, and other
 mechanisms.
 The ICMP and MPLS LSP PING applications SHOULD be rate-limited to
 below 5% of the bit-rate of the associated PW.  For this purpose, the
 considered bit-rate of a pseudowire is dependent on the PW type.  For
 pseudowires that carry constant bit-rate traffic (e.g., TDM PWs) the
 full bit-rate of the PW is used.  For pseudowires that carry variable
 bit-rate traffic (e.g., Ethernet PWs), the mean or sustained bit-rate
 of the PW is used.

Nadeau & Pignataro Standards Track [Page 23] RFC 5085 PW VCCV December 2007

 As described in Section 10, incoming VCCV messages can be rate-
 limited as a protection against denial-of-service attacks.  This
 throttling or policing of incoming VCCV messages should not be more
 stringent than the bandwidth allocated to the VCCV channel to prevent
 false indications of connectivity failure.

10. Security Considerations

 Routers that implement VCCV create a Control Channel (CC) associated
 with a pseudowire.  This control channel can be signaled (e.g., using
 LDP or L2TPv3 depending on the PWE3) or statically configured.  Over
 this control channel, VCCV Connectivity Verification (CV) messages
 are sent.  Therefore, three different areas are of concern from a
 security standpoint.
 The first area of concern relates to control plane parameter and
 status message attacks, that is, attacks that concern the signaling
 of VCCV capabilities.  MPLS PW Control Plane security is discussed in
 Section 8.2 of [RFC4447].  L2TPv3 PW Control Plane security is
 discussed in Section 8.1 of [RFC3931].  The addition of the
 connectivity verification negotiation extensions does not change the
 security aspects of Section 8.2 of [RFC4447], or Section 8.1 of
 [RFC3931].  Implementation of IP source address filters may also aid
 in deterring these types of attacks.
 A second area of concern centers on data-plane attacks, that is,
 attacks on the associated channel itself.  Routers that implement the
 VCCV mechanisms are subject to additional data-plane denial-of-
 service attacks as follows:
    An intruder could intercept or inject VCCV packets effectively
    providing false positives or false negatives.
    An intruder could deliberately flood a peer router with VCCV
    messages to deny services to others.
    A misconfigured or misbehaving device could inadvertently flood a
    peer router with VCCV messages which could result in denial of
    services.  In particular, if a router has either implicitly or
    explicitly indicated that it cannot support one or all of the
    types of VCCV, but is sent those messages in sufficient quantity,
    it could result in a denial of service.
 To protect against these potential (deliberate or unintentional)
 attacks, multiple mitigation techniques can be employed:
    VCCV message throttling mechanisms can be used, especially in
    distributed implementations which have a centralized control-plane

Nadeau & Pignataro Standards Track [Page 24] RFC 5085 PW VCCV December 2007

    processor with various line cards attached by some control-plane
    data path.  In these architectures, VCCV messages may be processed
    on the central processor after being forwarded there by the
    receiving line card.  In this case, the path between the line card
    and the control processor may become saturated if appropriate VCCV
    traffic throttling is not employed, which could lead to a complete
    denial of service to users of the particular line card.  Such
    filtering is also useful for preventing the processing of unwanted
    VCCV messages, such as those which are sent on unwanted (and
    perhaps unadvertised) control channel types or VCCV types.
    Section 8.1 of [RFC4447] discusses methods to protect the data
    plane of MPLS PWs from data-plane attacks.  However the
    implementation of the connectivity verification protocol expands
    the range of possible data-plane attacks.  For this reason
    implementations MUST provide a method to secure the data plane.
    This can be in the form of encryption of the data by running IPsec
    on MPLS packets encapsulated according to [RFC4023], or by
    providing the ability to architect the MPLS network in such a way
    that no external MPLS packets can be injected (private MPLS
    network).
    For L2TPv3, data packet spoofing considerations are outlined in
    Section 8.2 of [RFC3931].  While the L2TPv3 Session ID provides
    traffic separation, the optional Cookie field provides additional
    protection to thwart spoofing attacks.  To maximize protection
    against a variety of data-plane attacks, a 64-bit Cookie can be
    used.  L2TPv3 can also be run over IPsec as detailed in Section
    4.1.3 of [RFC3931].
 A third and last area of concern relates to the processing of the
 actual contents of VCCV messages, i.e., LSP Ping and ICMP messages.
 Therefore, the corresponding security considerations for these
 protocols (LSP Ping [RFC4379], ICMPv4 Ping [RFC0792], and ICMPv6 Ping
 [RFC4443]) apply as well.

11. Acknowledgements

 The authors would like to thank Hari Rakotoranto, Michel Khouderchah,
 Bertrand Duvivier, Vanson Lim, Chris Metz, W. Mark Townsley, Eric
 Rosen, Dan Tappan, Danny McPherson, Luca Martini, Don O'Connor, Neil
 Harrison, Danny Prairie, Mustapha Aissaoui, and Vasile Radoaca for
 their valuable comments and suggestions.

Nadeau & Pignataro Standards Track [Page 25] RFC 5085 PW VCCV December 2007

12. References

12.1. Normative References

 [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
            RFC 792, September 1981.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
            Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
            Encoding", RFC 3032, January 2001.
 [RFC3931]  Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
            Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
 [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
            Label Switched (MPLS) Data Plane Failures", RFC 4379,
            February 2006.
 [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
            "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
            Use over an MPLS PSN", RFC 4385, February 2006.
 [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
            Message Protocol (ICMPv6) for the Internet Protocol
            Version 6 (IPv6) Specification", RFC 4443, March 2006.
 [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
            Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
 [RFC4447]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
            Heron, "Pseudowire Setup and Maintenance Using the Label
            Distribution Protocol (LDP)", RFC 4447, April 2006.

12.2. Informative References

 [IANA.l2tp-parameters]
            Internet Assigned Numbers Authority, "Layer Two Tunneling
            Protocol "L2TP"", April 2007,
            <http://www.iana.org/assignments/l2tp-parameters>.
 [IANA.pwe3-parameters]
            Internet Assigned Numbers Authority, "Pseudo Wires Name
            Spaces", June 2007,
            <http://www.iana.org/assignments/pwe3-parameters>.

Nadeau & Pignataro Standards Track [Page 26] RFC 5085 PW VCCV December 2007

 [MSG-MAP]  Nadeau, T., "Pseudo Wire (PW) OAM Message Mapping",
            Work in Progress, March 2007.
 [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 2434,
            October 1998.
 [RFC3438]  Townsley, W., "Layer Two Tunneling Protocol (L2TP)
            Internet Assigned Numbers Authority (IANA) Considerations
            Update", BCP 68, RFC 3438, December 2002.
 [RFC3448]  Handley, M., Floyd, S., Padhye, J., and J. Widmer, "TCP
            Friendly Rate Control (TFRC): Protocol Specification",
            RFC 3448, January 2003.
 [RFC3916]  Xiao, X., McPherson, D., and P. Pate, "Requirements for
            Pseudo-Wire Emulation Edge-to-Edge (PWE3)", RFC 3916,
            September 2004.
 [RFC3985]  Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
            Edge (PWE3) Architecture", RFC 3985, March 2005.
 [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating
            MPLS in IP or Generic Routing Encapsulation (GRE)",
            RFC 4023, March 2005.
 [RFC4377]  Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
            Matsushima, "Operations and Management (OAM) Requirements
            for Multi-Protocol Label Switched (MPLS) Networks",
            RFC 4377, February 2006.
 [RFC4448]  Martini, L., Rosen, E., El-Aawar, N., and G. Heron,
            "Encapsulation Methods for Transport of Ethernet over MPLS
            Networks", RFC 4448, April 2006.
 [RFC4454]  Singh, S., Townsley, M., and C. Pignataro, "Asynchronous
            Transfer Mode (ATM) over Layer 2 Tunneling Protocol
            Version 3 (L2TPv3)", RFC 4454, May 2006.
 [RFC4928]  Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
            Cost Multipath Treatment in MPLS Networks", BCP 128,
            RFC 4928, June 2007.

Nadeau & Pignataro Standards Track [Page 27] RFC 5085 PW VCCV December 2007

Appendix A. Contributors' Addresses

 George Swallow
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxborough, MA 01719
 USA
 EMail: swallow@cisco.com
 Monique Morrow
 Cisco Systems, Inc.
 Glatt-com
 CH-8301 Glattzentrum
 Switzerland
 EMail: mmorrow@cisco.com
 Yuichi Ikejiri
 NTT Communication Corporation
 1-1-6, Uchisaiwai-cho, Chiyoda-ku
 Tokyo 100-8019
 Shinjuku-ku
 JAPAN
 EMail: y.ikejiri@ntt.com
 Kenji Kumaki
 KDDI Corporation
 KDDI Bldg. 2-3-2
 Nishishinjuku
 Tokyo 163-8003
 JAPAN
 EMail: ke-kumaki@kddi.com
 Peter B. Busschbach
 Alcatel-Lucent
 67 Whippany Road
 Whippany, NJ, 07981
 USA
 EMail: busschbach@alcatel-lucent.com

Nadeau & Pignataro Standards Track [Page 28] RFC 5085 PW VCCV December 2007

 Rahul Aggarwal
 Juniper Networks
 1194 North Mathilda Ave.
 Sunnyvale, CA 94089
 USA
 EMail: rahul@juniper.net
 Luca Martini
 Cisco Systems, Inc.
 9155 East Nichols Avenue, Suite 400
 Englewood, CO, 80112
 USA
 EMail: lmartini@cisco.com

Authors' Addresses

 Thomas D. Nadeau (editor)
 Cisco Systems, Inc.
 300 Beaver Brook Road
 Boxborough, MA  01719
 USA
 EMail: tnadeau@lucidvision.com
 Carlos Pignataro (editor)
 Cisco Systems, Inc.
 7200 Kit Creek Road
 PO Box 14987
 Research Triangle Park, NC  27709
 USA
 EMail: cpignata@cisco.com

Nadeau & Pignataro Standards Track [Page 29] RFC 5085 PW VCCV December 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Nadeau & Pignataro Standards Track [Page 30]

/data/webs/external/dokuwiki/data/pages/rfc/rfc5085.txt · Last modified: 2007/12/19 23:04 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki