Networking Working Group                                       D. Beller
Internet-Draft                                            Alcatel-Lucent
Intended Status: Standards Track                               A. Farrel
Created: March 5, 2009                                Old Dog Consulting
Expires: September 5, 2009

   An Inband Data Communication Network For the MPLS Transport Profile


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   A Generic Associated Channel (G-ACH) has been defined as an extension
   of the pseudowire Associated Channel Header (ACH) to enable the
   realization of a control/communication channel associated with
   Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs),
   MPLS pseudowires (PWs), MPLS LSP segments, and MPLS sections between
   adjacent MPLS-capable devices.

   The MPLS Transport Profile (MPLS-TP) is a profile of the MPLS
   architecture that identifies elements of the MPLS toolkit that may be
   combined to build a carrier grade packet transport network based on
   MPLS packet switching technology.

   This document describes how the G-ACH may be used to provide the
   infrastructure that forms part of the Management Communication
   Network (MCN) and a Signaling Communication Network (SCN).
   Collectively, the MCN and SCN may be referred to as the Data
   Communication Network (DCN). The document explains how MCN and SCN
   packets are encapsulated, carried on the G-ACH, and demultiplexed for

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   delivery to the management or signaling/routing components on a label
   switching router (LSR).

   It should be noted that the use of the G-ACH to provide connectivity
   for the DCN is intended for use only where the MPLS-TP network is not
   capable encapsulating or delivering native DCN messages.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   "OPTIONAL" in this document are to be interpreted as described in
   RFC-2119 [RFC2119].

1. Introduction

   The associated channel header (ACH) is specified in [RFC4385]. It is
   a packet header format for use on pseudowire (PW) packets in order to
   identify packets used for OAM and similar functions.

   The ACH is generalized for use on any Multiprotocol Label Switching
   (MPLS) Label Switching Path (LSP) in [GAL-GACH]. The generalized
   concept is referred to as the Generic Associated Channel (G-ACH) and
   is intended to create a control/communication channel associated with
   the LSP that can be used to carry packets used for OAM and similar
   functions (e.g. control plane messages).

   The purpose of a packet carried on the G-ACH is indicated by the
   value carried by the PW Associated Channel Type field of the G-ACH
   and a registry of values is maintained by IANA.

   The MPLS transport profile (MPLS-TP) is described in [MPLS-TP].
   MPLS-TP is the application of MPLS to construct a packet transport
   network. It constitutes a profile of MPLS that enables operational
   models typical in transport networks, which includes additional OAM,
   survivability and other maintenance functions not previously
   supported by MPLS.

   Label Switching Routers in MPLS networks may be operated using
   management protocols or control plane protocols. Messaging in these
   protocols is normally achieved using IP packets exchanged over IP-
   capable interfaces. However, some LSRs in MPLS-TP networks may be
   constructed without support for direct IP encapsulation on their
   line-side interfaces and without access to an out-of-fiber data
   communication network. In order that such LSRs can communicate using
   management plane or control plane protocols channels must be provided
   and the only available mechanism is to use an MPLS label.

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   The G-ACH provides a suitable mechanism, and this document defines
   processes and procedures to allow the G-ACH to be used to build a
   management communication network (MCN) and a signaling communication
   network (SCN) together known as the data communication network (DCN)

1.1. Requirements

   The requirements presented in this section are based on those
   communicated to the IETF by the ITU-T.

   1. A packet encapsulation mechanism must be provided to support the
      transport of MCN and SCN packets over the G-ACh.

   2. The G-ACh carrying the MCN and SCN packets shall support the
      following application scenarios:

      a. The G-ACh interconnects two adjacent MPLS-TP nodes (used when
         the server layer does not provide a Management Communication
         Channel (MCC) or a Signalling Communication Channel (SCC)).

      b. The G-ACh is carried by a MPLS-TP tunnel that traverses another
         operator's domain (carrier's carrier scenario)

   3. The G-ACh shall provide two independent channels: a MCC to build
      the MCN and a SCC to build the SCN. The G-ACh packet header shall
      indicate whether the packet is a MCC or an SCC packet in order to
      forward it to the management or control plane application for

   4. The channel separation mechanism shall allow the use of separate
      rate limiters and traffic shaping functions for each channel (MCC
      and SCC) ensuring that the flows do not exceed their assigned
      traffic profile. The rate limiter and traffic shaper are outside
      the scope of the MCC and SCC definition.

   5. The G-ACh that carries the MCC and SCC shall be capable of
      carrying different OSI layer 3 (network layer) PDUs. These shall
      include IPv4, IPv6, and OSI PDUs. The G-ACh header of the MCC/SCC
      packet shall indicate which layer 3 PDU is contained in the
      payload field of the packet such that the packet can be forwarded
      to the related layer 3 process within the management and control
      plane application, respectively, for further processing.

   6. The G-ACh is not required to provide specific security mechanisms.
      However, the management or control plane protocols that operate
      over the MCC or SCC are required to provide adequate security
      mechanisms in order not to be susceptible to security attacks.

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2. Procedures

   Figure 1 depicts the format of an MCC/SCC packet that is sent over
   the G-ACH. To send an MCC/SCC packet on the G-ACH, the MCC/SCC packet
   is prepended with the extended G-ACH header. This extended G-ACH
   header is composed of the G-ACH header as defined in [GAL-GACH] and
   is extended by four bytes providing an 8-bit protocol identifier
   (PID) field. The remaining 24 bits of the header extension are

    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|A|  Reserved   |         Channel Type          |
   |                    Reserved                   |      PID      |
   |                         MCC/SCC Packet                        |
   ~                                                               ~

         Figure 1: MCC/SCC Packet with Associated Channel Header

   o The Channel Type field determines whether the message is an MCC or
     an SCC message. See Section 4 for the codepoint assignments.

   o The PID field indicates the PDU type of the MCC/SCC message

     The following PID values are defined:

     0x00        IPv4
     0x01        IPv6
     0x02        OSI
     0x03-0xFF   Reserved

   Editor Note: This approach may be changed to use the G-ACH Protocol
   Identifier TLV if that work is progressed.

   If the PID is OSI, the first octet of the OSI PDU header (Network
   Layer Protocol Identifier) as defined in [ISO8473] indicates the
   network layer PDU which can be CLNP (0x81), ES-IS (0x82), or IS-IS
   (0x83) as specified in [ISO9577].

   When the G-ACH sender receives an MCC message from the management
   application that is supposed to be sent over the MCC, the sender
   creates the extended the G-ACH header depending on the MCC layer 3
   PDU, sets the Channel Type field to MCC, and prepends the MCC message

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   with the extended G-ACH header. The same procedure is applied when a
   control plane message is supposed to be sent over the SCC. In this
   case, the sender sets the Channel Type field to SCC.

   If the MPLS section G-ACH is used, the GAL is added to the packet as
   defined in [GAL-GACH], i.e.,  the TTL field SHOULD be set to 1, and
   the S-bit of the GAL MUST be set to 1.

   If the G-ACH is associated with an LSP, the GAL is added to the
   packet and the LSP label is pushed on top of the GAL as defined in
   [GAL-GACH], i.e., the TTL field of the GAL SHOULD be set to 1, and
   the S-bit of the GAL MUST be set to 1.

   It should be noted that the G-ACH MUST NOT be used to carry user data
   and SHALL only be used to carry management or control plane messages.
   Procedures that ensure this such as e.g. deep packet inspection are
   outside the scope of this specification.

   When a receiver has received a G-ACH packet with the G-ACH Channel
   Type set to MCC or SCC, it SHALL look at the PID field of the
   extended G-ACH header. If the PID value is known by the receiver it
   SHALL deliver the entire packet including the MCC/SCC message to the
   appropriate processing entity. If the PID value is unknown, the
   receiver SHALL silently discard the received Packet and MAY increment
   a counter that counts discarded packets.

   It must be noted that a receiver MUST NOT forward a GAL packet based
   on the GAL label as is normally the case for MPLS packets. If the GAL
   appears at the bottom of the label stack, it MUST be processed as
   described in the previous paragraph.

   Note that there is no requirement for MPLS-TP devices to support IP
   or OSI forwarding in the fast or slow paths. Thus, if a message is
   received on the MCC or SCC and is not targeted to an address of the
   receiving LSR, the LSR MAY discard the message as incorrectly

3. Security Considerations

   The G-ACH provides a virtual link between LSRs and might be used to
   induce many forms of security attack. Protocols that operate over the
   MCN or SCN are REQUIRED to include adequate security mechanisms and
   implementations MUST allow operators to configure the use of those

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4. IANA Considerations

   Channel Types for the Generic Associated Channel are allocated from
   the IANA PW Associated Channel Type registry defined in [RFC4446] and
   updated by [GAL-GACH].

   IANA is requested to allocate two further Channel Types as follows:

   xx  Management Communication Channel (MCC)
   yy  Signaling Communication Channel (SCC)

5. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4385]  Bryant, S., et al., "Pseudowire Emulation Edge-to-Edge
              (PWE3) Control Word for Use over an MPLS PSN", RFC 4385,
              February 2006.

   [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
              Emulation (PWE3)", RFC 4446, April 2006 .

   [GAL-GACH] Vigoureux, M., Bocci, M., Ward, D., Swallow, G., and R.
              Aggarwal, "MPLS Generic Associated Channel",
              draft-ietf-mpls-tp-gach-gal, work in progress.

6. Informative References

   [MPLS-TP]  Bryant, S., Bocci, M., Lasserre, M., "A Framework for MPLS
              in Transport Networks", draft-ietf-mpls-tp-framework, work
              in progress.

   [G.7712]  ITU-T Recommendation G.7712, "Architecture and
             specification of data communication network", June 2008.

   [ISO8473] ISO/IEC 8473-1, "Protocol for providing the connectionless-
             mode network service: Protocol specification - Part 1:
             ISO/IEC JTC 1/SC", 1998-11-01.

   [ISO9577] ISO/IEC TR 9577, "Protocol identification in the network
             layer ISO/IEC JTC 1/SC 6", 1999-12-15.

7. Acknowledgements

   The editors wish to thank Pietro Grandi and Martin Vigoureux for
   their contribution to this document.

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8. Authors' Addresses

   Dieter Beller
   Alcatel-Lucent Germany

   Adrian Farrel
   Old Dog Consulting

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