Subject: RE: [dhcwg] Methods of protecting DHCP relay-agent information op tions

From: "Woundy, Richard" <[email-masked]>
Date: Mon, 24 Feb 2003 16:28:16 -0700

John,

There might be one other minor consideration, that I stumbled across after
the Atlanta meeting. If DHCP Lease Query messages are implemented by the
relay agent, then IPSec encapsulation might be used to protect those
messages.

I cannot say that DHCP Lease Query is any more or less important than other
protocols on the relay agent. But at least it is a protocol under
consideration by *this* WG. ;^)

-- Rich

-----Original Message-----
From: John Schnizlein [mailto:[email-masked]]
Sent: Monday, February 24, 2003 4:16 PM
To: [email-masked]
Subject: [dhcwg] Methods of protecting DHCP relay-agent information
options

This is the summary I promised in Atlanta.

Two methods to protect the contents of the relay-agent information option
(RAIO) have been proposed: (1) encapsulating the DHCP message in IPsec
(RA-IPsec) [draft-droms-dhcp-relay-agent-ipsec-00.txt] and (2) including a
message authentication sub-option (AuthSO)
[draft-ietf-dhc-auth-suboption-01.txt] similar to the authentication option
for protecting options between clients and servers [RFC 3118]. Which method
is suitable depends on different circumstances.

Both methods employ keyed message authentication codes, and require
distribution of key material. Both methods must also support the separate
insertion of RAIO by a "trusted" device closer to the client and GIADDR by a
subsequent relay agent, specified in section 2.1 of RFC 3046. AuthSO
accommodates this separation the same way that RFC 3118 does, by excluding
mutable fields from the integrity computation. Because RA-IPsec necessarily
covers the entire message, it must establish IPsec security associations
(SA) between each pair of relay agents in the path as well as the SA between
the last relay agent and the DHC server. In circumstances where the
deployment of DHCP involves this separation of relay-agent function, the
RA-IPsec method would entail more configuration of these SAs than the
equivalent key management for AuthSO.

In circumstances where the "trusted" device requires protection for RAIO,
and does not already have the machinery for IPsec Encapsulating Security
Payload the AuthSO method might entail less implementation than RA-IPsec.
Where IPsec is already in all relay agents, the IPsec method would avoid
implementing AuthSO.

IPsec is based on existing protocols and technology, and can leverage key
distribution mechanisms and other future improvements.

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