Fail Over Extensions for Layer 2 Tunneling Protocol (L2TP) "failover"
RFC 4951

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Network Working Group                                       V. Jain, Ed.
Request for Comments: 4951                           Riverstone Networks
Category: Standards Track                                    August 2007

 Fail Over Extensions for Layer 2 Tunneling Protocol (L2TP) "failover"

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.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Layer 2 Tunneling Protocol (L2TP) is a connection-oriented protocol
   that has a shared state between active endpoints.  Some of this
   shared state is vital for operation, but may be volatile in nature,
   such as packet sequence numbers used on the L2TP Control Connection.
   When failure of one side of a control connection occurs, a new
   control connection is created and associated with the old connection
   by exchanging information about the old connection.  Such a mechanism
   is not intended as a replacement for an active fail over with some
   mirrored connection states, but as an aid for those parameters that
   are particularly difficult to have immediately available.  Protocol
   extensions to L2TP defined in this document are intended to
   facilitate state recovery, providing additional resiliency in an L2TP
   network, and improving a remote system's layer 2 connectivity.

Jain, et al.                Standards Track                     [Page 1]
RFC 4951                        FAILOVER                     August 2007

Table of Contents

   1. Introduction ....................................................3
      1.1. Terminology ................................................4
      1.2. Abbreviations ..............................................5
      1.3. Specification of Requirements ..............................5
   2. Overview ........................................................5
   3. Failover Protocol ...............................................7
      3.1. Failover Capability Negotiation ............................7
      3.2. Failover Recovery Procedure ................................7
           3.2.1. Recovery Tunnel Establishment .......................8
           3.2.2. Control Channel Reset ..............................10
           3.2.3. Data Channel Reset .................................10
      3.3. Session State Synchronization .............................11
   4. New Control Messages ...........................................12
      4.1. Failover Session Query ....................................13
      4.2. Failover Session Response .................................13
   5. New Attribute Value Pairs ......................................14
      5.1. Failover Capability AVP ...................................14
      5.2. Tunnel Recovery AVP .......................................15
      5.3. Suggested Control Sequence AVP ............................16
      5.4. Failover Session State AVP ................................17
   6. Configuration Parameters .......................................18
   7. IANA Considerations ............................................19
   8. Security Considerations ........................................19
   9. Acknowledgements ...............................................19
   10. Contributors ..................................................20
   11. References ....................................................20
      11.1. Normative References .....................................20
      11.2. Informative References ...................................20
   Appendix A ........................................................21
   Appendix B ........................................................23
   Appendix C ........................................................24

Jain, et al.                Standards Track                     [Page 2]
RFC 4951                        FAILOVER                     August 2007

1.  Introduction

   The goal of this document is to aid the overall resiliency of an L2TP
   endpoint by introducing extensions to RFC 2661 [L2TPv2] and RFC 3931
   [L2TPv3] that will minimize the recovery time of the L2TP layer after
   a failover, while minimizing the impact on its performance.
   Therefore, it is assumed that the endpoint's overall architecture is
   also supportive in the resiliency effort.

   To ensure proper operation of an L2TP endpoint after a failover, the
   associated information of the control connection and sessions between
   them must be correct and consistent.  This includes both the
   configured and dynamic information.  The configured information is
   assumed to be correct and consistent after a failover, otherwise the