DHCP Relay + PPP (your mail)

David W. Hankins David_Hankins at isc.org
Tue May 23 19:43:33 UTC 2006

On Tue, May 23, 2006 at 08:20:21PM +0100, Simon Hobson wrote:
> Any particular reason ? It is a valid relay configuration and only 
> has to handle unicast packets from the server on the PPP interface.

Largely because it doesn't make sense for a client or server to
operate DHCP on a ppp interface (more to the point, our BPF
interface doesn't understand the link layer...it would look
pretty silly spitting IEEE 802 down a ppp line).

> Pre-empting the answer I expect ... it's never seemed quite right to 
> me for the relay to have to listen in the same way on both 
> interfaces. On the interface(s) that are client facing, then yes, I 
> see the need for special handling to get the broadcast packets. But 
> surely it should be able to just open a normal socket on the server 
> facing interface(s) to handle the unicast packets.

Yeah, we need listen-only behaviour.

Really you want this behaviour reversed for relays - listen only on
the fallback standard BSD socket, and use the BPF etc sockets for

Some day that ship will come in.

David W. Hankins		"If you don't do it right the first time,
Software Engineer			you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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