Cisco Layer Two Forwarding (Protocol) "L2F"
RFC 2341
| Document | Type |
RFC - Historic
(May 1998; No errata)
Was draft-valencia-l2f (individual)
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|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | Legacy | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Stream | Legacy state | (None) | |
| Consensus Boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | RFC 2341 (Historic) | |
| Telechat date | |||
| Responsible AD | (None) | ||
| Send notices to | (None) | ||
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 [Page 1]
RFC 2341 Cisco L2F May 1998
4.1.2 Encapsulation of SLIP within L2F 10
4.2 L2F Packet Format 10
4.2.1 Overall Packet Format 10
4.2.2 Packet Header 11
4.2.3 Version field 11
4.2.4 Protocol field 11
4.2.5 Sequence Number 12
4.2.6 Packet Multiplex ID 12
4.2.7 Client ID 13
4.2.8 Length 13
4.2.9 Packet Checksum 13
4.2.10 Payload Offset 14
4.2.11 Packet Key 14
4.2.12 Packet priority 14
4.3 L2F Tunnel Establishment 14
4.3.1 Normal Tunnel Negotiation Sequence 15
4.3.2 Normal Client Negotiation Sequence 17
4.4 L2F management message types 18
4.4.1 L2F message type: Invalid 18
4.4.2 L2F_CONF 19
4.4.3 L2F_OPEN, tunnel establishment 20
4.4.4 L2F_OPEN, client establishment 20
4.4.5 L2F_CLOSE 22
4.4.6 L2F_ECHO 22
4.4.7 L2F_ECHO_RESP 23
4.5 L2F Message Delivery 23
4.5.1 Sequenced Delivery 23
4.5.2 Flow Control 23
4.5.3 Tunnel State Table 24
4.5.4 Client State Table 25
5.0 Protocol Considerations 26
5.1 PPP Features 26
5.2 Termination 26
5.3 Extended Authentication 26
5.4 MNP4 and Apple Remote Access Protocol 27
5.5 Operation over IP/UDP 27
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