From: P729 (p729@cox.net)
Date: Sat Jun 05 2004 - 20:06:10 GMT-3
Very odd. What version of IOS and platform are involved? 'ip
directed-broadcasts' are disabled by default in later versions of IOS and I
haven't had (or thought) to enable it when relaying DHCP lately...
Back in the day, NT didn't accept unicast DHCP requests so the helper target
had to be a directed (subnet) or all-nets broadcast--but I guess I never
thought of 'ip directed-broadcast' back then either since it was on by
default...
With 'ip directed-broadcast' off on the target interface, can you get a
debug to show the router accepting the broadcast but then just dropping it?
Maybe it'll give a reason.
Regards,
Mas Kato
https://ecardfile.com/id/mkato
----- Original Message -----
From: "Gregory W. Posey Jr." <gposey@uaes.org>
To: <ccielab@groupstudy.com>
Sent: Saturday, June 05, 2004 3:03 PM
Subject: IP Helper & Directed Broadcast
> Quick question A buddy of mine and I were discussing what happens when
you
> use IP Helper for DHCP, and we were wondering WHY there is a need to have
ip
> directed-broadcast turned on for the interface where the DHCP server is.
If
> the broadcast from the client gets converted to a unicast for the DHCP
> server, then where does directed-broadcast come into the picture.
>
> To top it off, he threw on a sniffer and verified that the traffic being
> sent to the DHCP server was unicast (in both the Layer 2 and Layer 3
senses
> of the word), yet when he disabled directed broadcasts, he was unable to
> obtain an IP address for his client.
>
> Any insights (or is it just the way that Cisco has implemented the
feature,
> no standards/technologies that actually make this necessary)?
>
> Thank you,
> Greg Posey Jr.
> CCIE #7981
> CCSP, CCSE
> M.S. EE
>
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