Subject: Source Port# for packets from BOOTP relay agent

From: Rob Stevens <[email-masked]>
Date: Mon, 25 Jun 2001 16:20:58 -0700

I had always assumed this should be port 67
yet I must admit that in no RFC is this
issue addressed.

Anyone have any strong opinion/recollection
about this?

My interest is primarily to install filters on
Cable Modems which would block
traffic emanating from port67 and then,
on the server, discard any packet which
purports to have been relayed but which
does not come from port67.

However a certain WK router manufacturer
has port68 as the source port, so this would
defeat the scheme.

Please note: I'm not talking about what port#
DHCP servers should use as the destination
port# when replying to relay agents. This
*MUST* be port 67.

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From: Ted Lemon <[email-masked]>
Date: Mon, 25 Jun 2001 19:33:05 -0700

It makes no sense for the relay agent to use port 68 as its source
port, since it doesn't listen on port 68.   So I would say that the
right thing is to use port 67, but I don't see how this helps you with
the router vendor that's doing it wrong.   :'(

			       _MelloN_

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From: [email-masked]
Date: Thu, 28 Jun 2001 17:55:55 -0400

From: Ted Lemon <[email-masked]>

Maybe it *is* listening on port 68, using it in a non-standard way.
That's icky, yes, but is it a violation of the protocol?

Dale
-- 
Dale R. WORLEY    Project Manager - UPnP        <[email-masked]>
Virata Corp.	  Applications Infrastructure   http://emweb.com

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From: Ted Lemon <[email-masked]>
Date: Thu, 28 Jun 2001 18:36:44 -0700

> Maybe it *is* listening on port 68, using it in a non-standard way.

Sure.   But it won't hear anything from a DHCP client on port 68.
The DHCP client sends its packets to port 67.   So it *must* listen on
port 67.   If it also listens on port 68, that has nothing to do with
what the DHCP protocol specification requires.

I can easily imagine a bridge that listens on port 68 and intercepts
packets on that port, but that's a hack, and someone who is doing a
hack like that should be doing their best to ensure that the thing
doesn't give away its presence by behaving in ways that aren't
apparently in accordance with the behaviour the protocol specificion
calls for.

			       _MelloN_

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From: Rob Stevens <[email-masked]>
Date: Thu, 28 Jun 2001 23:36:30 -0700

[email-masked] wrote:

>    ..

No, it doesn't appear to be. I was mildly surprised that it wasn't.
It's a nuisance though, and as Ted says is rather nonsensical,
because it's one more  filtering strategy that is now rendered invalid.