DHCP snooping on a relay agent

[malshara]

Hi all,

DHCP ==CLOUD ===2900 router ==== 3560 switch ---- PCs

I have configured DHCP snooping on the 3560 switch and 2900 router ,and configured the uplinks as a trusted interfaces ,but I have a clints connected to the router directly ,the router configured with ip-helper ,but the issue that when I enabled DHCP snooping on the 2900 router ,all the clients didn't get an IP address .

my question :Is it possible to configure DHCP snooping on the 2900 router while ip-helper configured on it ?

Thanks in advance

Regards

[Masoud Pourshabanian · Accepted solution]

Hello,

Try these two commands. Your problem should be solved only with one of them. Please give me feedback.

On router:

ip dhcp relay information trust-all

on switch :

no ip dhcp snooping information option

Hope it helps,

Masoud

[malshara]

Hi Masoud,

thanks for your answer ,even ip dhcp relay information trust-all solved the issue ,but I can see that there are no option 82 configuration on both sides ,the switch and the router . :) .

so what is happening here :) ,I will try to get a sniffer capture and check if the giaddr= =0 .

thanks in advance

Regards

[Masoud Pourshabanian]

Hello,

Switch adds option 82 and sets giaddr to 0.0.0.0 on dhcp messages when you activate snooping. Router receives those messages and drops them. 

I am glad your problem was solved.

Masoud.