RFC 2341 (rfc2341) - Page 1 of 29

Cisco Layer Two Forwarding (Protocol) "L2F"

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Network Working Group                                         A. Valencia
Request for Comments: 2341                                  M. Littlewood
Category: Historic                                               T. Kolar
                                                            Cisco Systems
                                                                 May 1998


              Cisco Layer Two Forwarding (Protocol) "L2F"

Status of Memo

   This memo describes a historic protocol for the Internet community.
   It does not specify an Internet standard of any kind.  Distribution
   of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   Virtual dial-up allows many separate and autonomous protocol domains
   to share common access infrastructure including modems, Access
   Servers, and ISDN routers.  Previous RFCs have specified protocols
   for supporting IP dial-up via SLIP [1] and multiprotocol dial-up via
   PPP [2].  This document describes the Layer Two Forwarding protocol
   (L2F) which permits the tunneling of the link layer (i.e., HDLC,
   async HDLC, or SLIP frames) of higher level protocols.  Using such
   tunnels, it is possible to divorce the location of the initial dial-
   up server from the location at which the dial-up protocol connection
   is terminated and access to the network provided.

Table of Contents

   1.0 Introduction                                                3
   1.1 Conventions                                                 3
   2.0 Problem Space Overview                                      3
   2.1 Initial Assumptions                                         3
   2.2 Topology                                                    4
   2.3 Virtual dial-up Service - a walk-though                     5
   3.0 Service Model Issues                                        7
   3.1 Security                                                    7
   3.2 Address allocation                                          8
   3.3 Authentication                                              8
   3.4 Accounting                                                  8
   4.0 Protocol Definition                                         9
   4.1 Encapsulation within L2F                                   10
   4.1.1 Encapsulation of PPP within L2F                          10



Valencia, et. al.               Historic
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