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 2001Table 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
datatracker.ietf.org