Intermittent DCHP on Cisco 9500

[Alcides Miguel]

Hello,

We are facing intermittent DHCP for clients traversing the Cisco Switch 9500.

Diagram:

Windows Client---->Access Switch---->CORE Switch (9500)---->DHCP Server.

From the debug I see packets being sent to the DHCP server, and clients sometimes can get IP addresses and sometimes not. I was reading the link bellow: https://www.cisco.com/c/en/us/support/docs/switches/catalyst-9300-series-switches/217429-troubleshoot-slow-or-intermittent-dhcp-o.html#toc-hId-1052385255

Interface configuration

And a disabled "ip redirects" on interfaces which has "ip helper-address" configured, but I still see huge ICMP redirects on "show platform hardware fed switch active qos queue stats internal cpu policer" command

[marce1000]

   - @Alcides Miguel   (core) Switches are never ideal for DHCP because of the traffic load which they sometimes need to prioritize, consider using an appliance for DHCP servers. Sometimes vendors will also offer a redundant 'DHCP cluster', (2 nodes) always preserving a copy for the lease database (e.g.)

   M.

[Alcides Miguel]

Hello @marce1000 

Thanks for your response.

I'm not using the core switch as the DHCP server, it's being held by a Windows Server. The (core) switch is doing DHCP Relay.

[Jens Albrecht]

Hello @Alcides Miguel,

you mentioned that you 'disabled "ip redirects" on interfaces which has "ip helper-address" configured' which sounds to me that you might also have some IP interfaces on your core switch that do not have the "ip helper-address" command set.

For the CPU and CoPP it does not make any difference on which interface the redirects are generated. So if other interfaces still generate redirects, then your DHCP traffic can still be affected which simply means it gets dropped.

In that case you should disable redirects on all interfaces and then check whether the drop counter continues to increase.

HTH!