Network Working Group M. Richardson
Internet-Draft SSW
Expires: August 17, 2003 February 16, 2003
A method for configuration of IPsec clients using DHCP
draft-richardson-ipsec-dhcp-over-ike-00.txt
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Copyright (C) The Internet Society (2003). All Rights Reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Time sequence diagram . . . . . . . . . . . . . . . . . . . . . 5
3. Comparisons with mode-cfg . . . . . . . . . . . . . . . . . . . 6
4. Comparisons with DHCP-over-IPsec . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 9
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Abstract
IPsec technology is frequently used for remote access scenarios. A
tunnel is established from a mobile node (such as a laptop) and an
IPsec gateway located at the Enterprise. The mobile node's tunnel
outer address is potentially any IP address on the Internet. The
mobile node's tunnel inner address should be an address from within
the enterprise. The assignment of this address should ideally be
done dynamically.
This document specifies a configuration mode called "DHCP over IKE".
The document specifies that the payload of a DHCP exchange should be
carried over an IKE phase 1 exchange.
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1. Introduction
Intro about problem space for configuring clients with addresses. We
use [1] to with [2].
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2. Time sequence diagram
The setup consists of:
+--------+ +---------+ +--------+
| client |=================| Security|---------| DHCP |
+--------+ | gateway | | server |
+---------+ +--------+
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ]
HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, DHCP(disc)} -->
---DHCP Discovery->
<--DHCP Offer------
<-- HDR, SK {IDr, [CERT,] AUTH, DHCP(offer))}
HDR, SK{SAi2, TSi, TSr, DHCP(request)}-->
---DHCP request-->
<--DHCP ACK-------
<-- HDR, SK {SAr2, TSi, TSr, DHCP(ack)}
later, upon rekey, one does:
HDR, SK {SAi2, TSi, TSr, DHCP(request)}-->
---DHCP request-->
<--DHCP ACK-------
<-- HDR, SK {SAr2, TSi, TSr, DHCP(ack)}
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3. Comparisons with mode-cfg
From the point of view of the IKE implementor, this proposal is very
similar to mode configuration. There are two major differences:
inclusion of a DHCP client state machine into the client IKE, and the
IKEv2 gateway must encapsulate the DHCP payloads into a UDP packet
and relay them to a DHCP server. The gateway SHOULD also append DHCP
relay options to the end to signal to the DHCP server that it came
via IKEv2.
The major advantage of DHCP-over-IKE vs mode-cfg is that it leverages
all of the DHCP protocol infrastructure for configuration of the end
host. Further, it naturally interacts with the DHCP infrastructure
at the enterprise end.
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4. Comparisons with DHCP-over-IPsec
The DHCP-over-IKE situation appears more complicated due to the
inclusion of the DHCP state machines into IKEv2. The major
complexity appears to be on the client. Note that this is an
illusion - in the DHCP-over-IPsec, the IKE on the client needs to
know what state the DHCP client it is so that it may act accordingly.
As such, the states are simply represented twice. Unless the
implementor is able to take advantage of an existing DHCP client
present on the OS, there is little savings in actual code.
DHCP-over-IPsec requires that a very strange IPsec SA be configured
for: 0.0.0.0/0:udp/67 <->0.0.0.0/0:udp/68. Note that extreme care
must be taken to make sure that this does not also catch packets
destined to the DHCP server on the physical wire. This SA MUST be be
torn down before any traffic is mis-directed on it. Further, it is
very difficult to configure a mobile system that must maintain
tunnels to two enterprises.
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References
[1] Droms, R., "Dynamic Host Configuration Protocol", RFC 1531,
October 1993.
[2] Maughan, D., Schneider, M. and M. Schertler, "Internet Security
Association and Key Management Protocol (ISAKMP)", RFC 2408,
November 1998.
Author's Address
Michael C. Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z 5V7
CA
EMail: mcr@sandelman.ottawa.on.ca
URI: http://www.sandelman.ottawa.on.ca/
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