DHCP Relay Agent Information Option
RFC 3046

Network Working Group                                         M. Patrick
Request for Comments: 3046                                  Motorola BCS
Category: Standards Track                                   January 2001

                  DHCP Relay Agent Information Option

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 (2001).  All Rights Reserved.

Abstract

   Newer high-speed public Internet access technologies call for a
   high-speed modem to have a local area network (LAN) attachment to one
   or more customer premise hosts.  It is advantageous to use the
   Dynamic Host Configuration Protocol (DHCP) as defined in RFC 2131 to
   assign customer premise host IP addresses in this environment.
   However, a number of security and scaling problems arise with such
   "public" DHCP use.  This document describes a new DHCP option to
   address these issues.  This option extends the set of DHCP options as
   defined in RFC 2132.

   The new option is called the Relay Agent Information option and is
   inserted by the DHCP relay agent when forwarding client-originated
   DHCP packets to a DHCP server.  Servers recognizing the Relay Agent
   Information option may use the information to implement IP address or
   other parameter assignment policies.  The DHCP Server echoes the
   option back verbatim to the relay agent in server-to-client replies,
   and the relay agent strips the option before forwarding the reply to
   the client.

   The "Relay Agent Information" option is organized as a single DHCP
   option that contains one or more "sub-options" that convey
   information known by the relay agent.  The initial sub-options are
   defined for a relay agent that is co-located in a public circuit
   access unit.  These include a "circuit ID" for the incoming circuit,
   and a "remote ID" which provides a trusted identifier for the remote
   high-speed modem.

Patrick                     Standards Track                     [Page 1]
RFC 3046          DHCP Relay Agent Information Option       January 2001

Table of Contents

   1   Introduction...........................................  2
   1.1 High-Speed Circuit Switched Data Networks..............  2
   1.2 DHCP Relay Agent in the Circuit Access Equipment.......  4
   2.0 Relay Agent Information Option.........................  5
   2.1 Agent Operation........................................  6
   2.1.1 Reforwarded DHCP requests............................  7
   2.2 Server Operation.......................................  7
   3.0 Relay Agent Information Suboptions.....................  8
   3.1 Agent Circuit ID.......................................  8
   3.2 Agent Remote ID........................................  9
   4.0 Issues Resolved........................................  9
   5.0 Security Considerations................................ 10
   6.0 IANA Considerations.................................... 11
   7.0 Intellectual Property Notice........................... 12
   8.0 References............................................. 12
   9.0 Glossary............................................... 13
   10.0 Author's Address...................................... 13
   11.0 Full Copyright Statement ............................. 14

1   Introduction

1.1 High-Speed Circuit Switched Data Networks

   Public Access to the Internet is usually via a circuit switched data
   network.  Today, this is primarily implemented with dial-up modems
   connecting to a Remote Access Server.  But higher speed circuit
   access networks also include ISDN, ATM, Frame Relay, and Cable Data
   Networks.  All of these networks can be characterized as a "star"
   topology where multiple users connect to a "circuit access unit" via
   switched or permanent circuits.

   With dial-up modems, only a single host PC attempts to connect to the
   central point.  The PPP protocol is widely used to assign IP
   addresses to be used by the single host PC.

   The newer high-speed circuit technologies, however, frequently
   provide a LAN interface (especially Ethernet) to one or more host
   PCs.  It is desirable to support centralized assignment of the IP
   addresses of host computers connecting on such circuits via DHCP.
   The DHCP server can be, but usually is not, co-implemented with the
   centralized circuit concentration access device.  The DHCP server is