High-Level Data Link Control (HDLC) Frames over Layer 2 Tunneling Protocol, Version 3 (L2TPv3)
RFC 4349

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Network Working Group                                       C. Pignataro
Request for Comments: 4349                                   M. Townsley
Category: Standards Track                                  Cisco Systems
                                                           February 2006

              High-Level Data Link Control (HDLC) Frames
          over Layer 2 Tunneling Protocol, Version 3 (L2TPv3)

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 Internet Society (2006).

Abstract

   The Layer 2 Tunneling Protocol, Version 3, (L2TPv3) defines a
   protocol for tunneling a variety of data link protocols over IP
   networks.  This document describes the specifics of how to tunnel
   High-Level Data Link Control (HDLC) frames over L2TPv3.

Pignataro & Townsley        Standards Track                     [Page 1]
RFC 4349                HDLC Frames over L2TPv3            February 2006

Table of Contents

   1. Introduction ....................................................2
      1.1. Abbreviations ..............................................2
      1.2. Specification of Requirements ..............................3
   2. Control Connection Establishment ................................3
   3. HDLC Link Status Notification and Session Establishment .........3
      3.1. L2TPv3 Session Establishment ...............................3
      3.2. L2TPv3 Session Teardown ....................................5
      3.3. L2TPv3 Session Maintenance .................................5
      3.4. Use of Circuit Status AVP for HDLC .........................6
   4. Encapsulation ...................................................6
      4.1. Data Packet Encapsulation ..................................6
      4.2. Data Packet Sequencing .....................................7
      4.3. MTU Considerations .........................................7
   5. Applicability Statement .........................................8
   6. Security Considerations .........................................9
   7. IANA Considerations .............................................9
      7.1. Pseudowire Type ............................................9
      7.2. Result Code AVP Values .....................................9
   8. Acknowledgements ................................................9
   9. References .....................................................10
      9.1. Normative References ......................................10
      9.2. Informative References ....................................10

1.  Introduction

   [RFC3931] defines a base protocol for Layer 2 Tunneling over IP
   networks.  This document defines the specifics necessary for
   tunneling HDLC Frames over L2TPv3.  Such emulated circuits are
   referred to as HDLC Pseudowires (HDLCPWs).

   Protocol specifics defined in this document for L2TPv3 HDLCPWs
   include those necessary for simple point-to-point (e.g., between two
   L2TPv3 nodes) frame encapsulation, and for simple interface up and
   interface down notifications.

   The reader is expected to be very familiar with the terminology and
   protocol constructs defined in [RFC3931].

1.1 Abbreviations

   HDLC    High-Level Data Link Control
   HDLCPW  HDLC Pseudowire
   LAC     L2TP Access Concentrator (see [RFC3931])
   LCCE    L2TP Control Connection Endpoint (see [RFC3931])
   PW      Pseudowire

Pignataro & Townsley        Standards Track                     [Page 2]
RFC 4349                HDLC Frames over L2TPv3            February 2006

1.2.  Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  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.  Control Connection Establishment

   In order to tunnel an HDLC link over IP using L2TPv3, an L2TPv3
   Control Connection MUST first be established as described in
   [RFC3931].  The L2TPv3 SCCRQ Control Message and corresponding SCCRP
   Control Message MUST include the HDLC Pseudowire Type of 0x0006 (see
   Section 7, "IANA Considerations"), in the Pseudowire Capabilities
   List as defined in 5.4.3 of [RFC3931].  This identifies the control
   connection as able to establish L2TP sessions to support HDLC
   Pseudowires (HDLCPWs).

   An LCCE MUST be able to uniquely identify itself in the SCCRQ and
   SCCRP messages via a globally unique value.  By default, this is
   advertised via the structured Router ID AVP [RFC3931], though the