5520 not forwarding DHCP offer

[brazenhead]

Hi, I'm seeing some odd behavior on one of my 5520's: there was a power outage today and when the 5520 came back up, the connected devices were no longer able to obtain an ip addresses. The devices can send a DHCP discover and the DHCP server responds with a DHCP offer and that is where the communication ends. Either the DHCP offer from the server is not getting back to the client or the DHCP ACK from the client is not getting back to the server. I'll probably just replace the switch and see if I can figure out what's happening with it later, but has anyone ever see this type of issue before?

Thanks.

[Jon Hurtt]

Never seen this issue before, since DHCP is just a broadcast packet, are you having problems with any other types of traffic? Are you running DHCP Snooping or ARP Inspection?  Let us know how it goes...

[brazenhead]

I'm not on site so it's pretty hard to tell exactly what is going on ... I can see that no-one has been able to get an ip address therefore the devices are not sending out much for traffic other than DHCP discovers (I see this on our DHCP server). We are not running DHCP Snooping or ARP Inspection. I can get to the switches on the management network no prob. I think I'll have to get onsite to get some addional info.

[brazenhead]

Also, are the DHCP offer and ack unicast or broadcast if the traffic crosses subnets? The dhcp server is on a different network. dhcp relay set up on the core 8600.

[Jon Hurtt]

It will be unicast if you are using DHCP Relay...

[Michael McNamara]

I've had this issue on 5.1.x software... had to delete the DHCP relay and then re-create it again to get things working again.

I believe there is a command in 6.x software which you can use to get the dhcp-relay statistics.

Good Luck!

[brazenhead]

Found out what the problem was - somehow the power outage corrupted the configuration of the 5530 distribution switch that the above mentioned 5520 stack is connected to via MLT. On the 5530, the MLT configuration had vanished but the 5520 thought it was still MLT'd (which it was physically). Anyway, the broadcast  dhcp discover from the clients were making it to the dhcp server, but the dhcp offer was not making it back to any clients that were communicating on one link of the MLT.  Kind of hard to explain - if you are truely interested let me know and I'll go into more details. Anyway, as soon I recreated the MLT on the 5530, everyone started working again.

Thanks for the responses.

[KT]

Need to note in the bible for feature preference...............

cheers!!!!!!!