Subject: [dhcwg] RFC 3046 in conjunction with RFC 3396

From: "Kostur, Andre" <[email-masked]>
Date: Tue, 18 Jan 2005 16:48:01 -0800

Let's assume that some relay between the client and the DHCP server adds in
option 82 with a Circuit ID (say, "eth0"), and a Remote ID (say, the MAC
address of the device).  Let's also assume that the relay is depending on
RFC 3396 behaviour, and puts that into the packet as (byte values, or ASCII
character value as appropriate):

82 6 1 4 'e' 't' 'h' '0' 82 8 2 6 0 1 2 3 4 5

and is depending on the service to correctly concatenate them together to
form the option:

82 14 1 4 'e' 't' 'h' '0' 8 2 6 0 1 2 3 4 5

The service does all of the processing as appropriate, and sends back an
Offer/Ack.

Should the relay expect the fragmented version of option 82 to be in the
packet, or should the relay be able to handle either the fragmented or the
completely assembled option to be at the end of the packet?

I guess a re-phrased version of the question: if the relay inserts a
fragmented option 82 into a packet (in accordance with 3396), should the
relay expect the identically fragmented option 82 in the return packet, or
is the service allowed to fragment the packet in a different manner
(including completely reassembling the option if the aggregate length is
short enough)?
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From: "Bernie Volz" <[email-masked]>
Date: Tue, 18 Jan 2005 20:07:08 -0500

I would suggest that the relay accept either -- the relay should
concatentate the option.
 
Note that the relay may also not care about the contents of the option --
all it is required to do is to remove any 82 options.
 
- Bernie

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Kostur, Andre
Sent: Tuesday, January 18, 2005 7:48 PM
To: [email-masked]'
Subject: [dhcwg] RFC 3046 in conjunction with RFC 3396

---

From: Ted Lemon <[email-masked]>
Date: Tue, 18 Jan 2005 20:29:27 -0700

On Jan 18, 2005, at 5:48 PM, Kostur, Andre wrote:
> fragmented option 82 into a packet (in accordance with 3396), should 
> the relay expect the identically fragmented option 82 in the return 
> packet, or is the service allowed to fragment the packet in a 
> different manner (including completely reassembling the option if the 
> aggregate length is short enough)?

It would be extremely optimistic to count on either behavior.   Both 
are certainly possible.   To follow the standard, I would suggest that 
the relay should be prepared to do concatenation on its relay agent 
information option if it wants to send a split option.   However, since 
option 82 doesn't reference the concatenation draft, it's not safe to 
assume that recipients of option 82 will know how to handle a split 
option 82, so in fact, it would be against common sense to ever send a 
split option 82.   Unfortunately, the option concatenation RFC doesn't 
specifically forbid this, because I didn't think of it, nor did anyone 
who reviewed the drafts prior to RFC.   :'(