Extensions to Support Efficient Carrying of Multicast Traffic in Layer-2 Tunneling Protocol (L2TP)
RFC 4045

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• 05

Network Working Group                                         G. Bourdon
Request for Comments: 4045                                France Telecom
Category: Experimental                                        April 2005

             Extensions to Support Efficient Carrying of
        Multicast Traffic in Layer-2 Tunneling Protocol (L2TP)

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   The Layer Two Tunneling Protocol (L2TP) provides a method for
   tunneling PPP packets.  This document describes an extension to L2TP,
   to make efficient use of L2TP tunnels within the context of deploying
   multicast services whose data will have to be conveyed by these
   tunnels.

Table of Contents

   1.  Introduction..................................................  2
       1.1.  Conventions Used in This Document.......................  3
       1.2.  Terminology.............................................  3
   2.  Motivation for a Session-Based Solution.......................  4
   3.  Control Connection Establishment..............................  5
       3.1.  Negotiation Phase.......................................  5
       3.2.  Multicast Capability AVP (SCCRQ, SCCRP).................  5
   4.  L2TP Multicast Session Establishment Decision.................  6
       4.1.  Multicast States in LNS.................................  6
       4.2.  Group State Determination...............................  8
       4.3.  Triggering..............................................  9
       4.4.  Multicast Traffic Sent from Group Members............... 10
   5.  L2TP Multicast Session Opening Process........................ 11
       5.1.  Multicast-Session-Request (MSRQ)........................ 11
       5.2.  Multicast-Session-Response (MSRP)....................... 12
       5.3.  Multicast-Session-Establishment (MSE)................... 12
   6.  Session Maintenance and Management............................ 13
       6.1.  Multicast-Session-Information (MSI)..................... 13
       6.2.  Outgoing Sessions List Updates.......................... 14

Bourdon                       Experimental                      [Page 1]
RFC 4045          Efficient Multicast Traffic in L2TP         April 2005

             6.2.1.  New Outgoing Sessions AVP (MSI)................. 15
             6.2.2.  New Outgoing Sessions Acknowledgement AVP (MSI). 15
             6.2.3.  Withdraw Outgoing Sessions AVP (MSI)............ 17
       6.3.  Multicast Packets Priority AVP (MSI).................... 17
             6.3.1.  Global Configuration............................ 18
             6.3.2.  Individual Configuration........................ 19
             6.3.3.  Priority........................................ 19
   7.  Multicast Session Teardown.................................... 19
       7.1.  Operations.............................................. 20
       7.2.  Multicast-Session-End-Notify (MSEN)..................... 20
       7.3.  Result Codes............................................ 21
   8.  Traffic Merging............................................... 22
   9.  IANA Considerations........................................... 22
   10. Security Considerations....................................... 23
   11. References.................................................... 23
       11.1. Normative References.................................... 23
       11.2. Informative References.................................. 24
   12. Acknowledgements.............................................. 24
   Appendix A.  Examples of Group States Determination............... 25
   Author's Address.................................................. 27
   Full Copyright Statement.......................................... 28

1.  Introduction

   The deployment of IP multicast-based services may have to deal with
   L2TP tunnel engineering.  The forwarding of multicast data within
   L2TP sessions may impact the throughput of L2TP tunnels because the
   same traffic may be sent multiple times within the same L2TP tunnel,
   but in different sessions.  This proposal aims to reduce the impact
   by applying the replication mechanism of multicast traffic only when
   necessary.

   The solution described herein provides a mechanism for transmitting
   multicast data only once for all the L2TP sessions that have been
   established in a tunnel, each multicast flow having a dedicated L2TP
   session.

   Within the context of deploying IP multicast-based services, it is
   assumed that the routers of the IP network that embed a L2TP Network
   Server (LNS) capability may be involved in the forwarding of
   multicast data, toward users who access the network through an L2TP