DHCP snooping

Unanswered Question
Feb 24th, 2008

Hello All,

I faced the following issue:

My 3560 switch is connected to 3750 stacked switch with a trunk port - over a Metro ethernet line - using Vlan 100 as native vlan. DHCP servers are connected to 3750 with two NICs, on 3560 and 3750 the dhcp snooping is enabled, ports connected to DHCP servers are trusted on 3750 and the uplink to 3750 on 3560 is also trusted. I use windows 2003 DHCP service and IP Option 82 is disabled on both devices. The default gateway of our Workstation lan is on 3560 and the DHCP requests are redirected to the DHCP server with the ip helper-address. What I see on the debug is that so many DHCPDISCOVER message is sent by the client but no offer received.

PC client - untrusted 3560 trusted - untrusted 3750 trusted - DHCP server

Snooping is configured on both devices as follow:

ip dhcp snooping

ip dhcp snooping vlan 100-200

no ip dhcp snooping information option

trusted interface

ip dhcp snooping trust

PC VLAN likes:

interface vlan 150

ip address 10.x.x.x

ip helper-address 10.x.y.x

What can be the root cause?

I guess the best is deploy DHCP snooping not only at access-layer but distribution as well.

Thanks your help in advance,



I have this problem too.
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