From: Murphy, William (William.Murphy@uth.tmc.edu)
Date: Thu Apr 17 2008 - 13:42:12 ART
We turned off the information option because our DHCP server does not
support it, although I suppose the server would have just ignored the
option had we done the trust option... Are you guys actually using a
DHCP server that supports it? Thanks...
Bill Murphy
Senior Network Analyst
University of Texas Health Science Center - Houston
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Rik Guyler
Sent: Thursday, April 17, 2008 10:47 AM
To: 'Geert Nijs'; ccielab@groupstudy.com
Subject: RE: DHCP snooping
Thanks Geert. I tried suggestions that both Sadiq and William made and
got
this thing to work but I'm going to play around with your suggestion as
well
now that I know the option 82 thing is the culprit. I'm not running
DHCP on
the switch directly so didn't try a DHCP server debug but I'll give it a
shot anyway and see what I get.
Thanks again!
Rik
-----Original Message-----
From: Geert Nijs [mailto:Geert.Nijs@simac.be]
Sent: Thursday, April 17, 2008 11:36 AM
To: Rik Guyler; ccielab@groupstudy.com
Subject: RE: DHCP snooping
Rik,
Check this. It is actually Option82 insertion that is breaking DHCP when
you
enable DHCP snooping. There has been previous posts to cciegroup and i
myself have also
spend 1 day at debugging the issue.......
If you add the "ip dhcp relay information trusted" on the SVI interfaces
that have the IP helper address defined, this
command allows the L3 interface to forward packets that include DHCP
Option
82 informations (which DHCP snooping does by default). Without the line,
the
interface
will not forward dhcp request to the iphelper destination.
On the device doing the forwarding "debug ip dhcp server" will give the
error "relay information exists, but giaddr is zero", and the packet
will
not be forwarded.
regards,
Geert
CCIE#13729
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