Subject: RE: [dhcwg] Clarification on RFC 2131 and RFC 3046

From: "Kostur, Andre" <[email-masked]>
Date: Tue, 14 Jan 2003 07:57:54 -0800

Sorry, I don't see how that clarifies.  From my original message :

Regarding the use of the Client Identifier option to identify a specific
device: 

RFC 2131, Section 4.2 suggests that a DHCP server should use the Client
Identifier supplied by the client device where possible, and to effectively
synthesize one from the client's chaddr if the client does not supply one.
(Actually, section 4.2 insists that a server uses the Client Identifier, if
supplied).

RFC 3046, Section 4.0 seems to downplay the use of the Client Identifier and
encourages the combination of RemoteID and CHADDR to distinguish a device.
If the use of a Client Identifier is discouraged, how would a device acquire
multiple IP addresses from the DHCP server, since the server is encouraged
to only use the RemoteID and CHADDR?  (Perhaps we're talking about a set-top
box that can do VoIP, and digital video.  The device may want an IP for
Voice, and a second IP for video, but only has 1 MAC address...?)

Let's assume a physical setup of:

DHCP <----> Router/Relay <----> Multifunction Device (MFD)

And assume that the MFD has 1 ethernet card, but has three "services" each
of which want an IP.  According to how RFC 3046 reads, the DHCP service
should try to distinguish the device by looking at only two things: the
Remote ID (since all the requests are passing through the same relay,
they're all coming from the same Remote ID), and the CHADDR (since all the
requests are originating from the same Ethernet card, they're all coming
from the same CHADDR).  With only those two criteria, the DHCP server would
see the _same_ device requesting 3 times, and would ACK with the same IP
address three times.  If RFC 3046 allowed (and/or insisted) on the same
process as RFC 2131 (using the Client Identifier), the MFD could change the
Client Identifier supplied with each request so that the DHCP server would
interpret the 3 incoming Discovers as actually being discovers for 3
different addresses (since from DHCP's point of view, it would be 3 distinct
devices requesting).

> -----Original Message-----
> From: Ted Lemon [mailto:[email-masked]]
> Sent: Monday, January 13, 2003 7:29 PM
> To: Kostur, Andre
> Cc: [email-masked]'
> Subject: Re: [dhcwg] Clarification on RFC 2131 and RFC 3046
> 
> 
> Remote-id identifies the relay agent, not the DHCP client.
>

---

From: Ted Lemon <[email-masked]>
Date: Tue, 14 Jan 2003 23:51:56 -0600

The remote ID is part of the relay agent information option, which is 
sent by the *relay agent*, not by the client.   The client *never* 
sends the relay agent information option, and thus *never* sends a 
remote ID.   So if you are trying to identify the client, you 
absolutely *cannot* use the remote ID to do it, because it didn't come 
from the client.

When RFC3046 talks about using the remote ID to identify a device, it 
is not talking about the DHCP client - it is talking about the DHCP 
relay agent.   The two RFCs are talking about different things, and 
thus are not at all in conflict.

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