upgrade ms225's 9.32 -> 9.36 and multiple DHCP servers?

[joopv]

We have a network of multiple MS225 switches, divided over 5 stacks.  These are L2 only (supposedly 😞 ).  There are 2 DHCP servers and a DHCP forwarder active, running on 2 Cisco routers which have a HSRP connection to the Meraki switches, and divided over the different L2 vlan's

After upgrading from 9.32 to 9.36 we started having DHCP problems.  In the end, we had to disable one of the 2 Cisco routers completely, thereby also disabling the redundancy setup.

DHCP server policy is "allowed" .

I wonder if there is an explanation for this beheavior?

[Adam]

You will likely need to do some captures and I've also found DHCPExplorer useful for helping troubleshoot DHCP issues.  

And you said Switch>DHCP Servers shows what you'd expect to see?

[joopv]

Thanks for your reply.

We did captures at the time of the issue.  We could see packets being forwarded (ip helper) to the DHCP server - and coming back to the client on the meraki network.  DHCP information was however never received by the client.

This post is just to ask if there is someone with similar experiences.

[Adam]

I understand.  When you say the DHCP coming back to the client on the Meraki network was it actually observed on the port the client was connected to?  Use Wireshark on a client to see what is observed there?  I'm just curious where the breakdown occurred. 

[joopv]

The DHCP activity was observed on the Cisco router forwarding or replying on the DHCP requests (debug ip dhcp server packet).  We did do a packet capture on the Meraki switches, but there the clients did not receive the info.

So we have the info that the router claims the dhcp reply was send, but the Meraki switch claims not to receive this reply...

[Adam]

Seems like it would be diagnostically valuable to do captures on each hop in between the router and the client switch port to see where the packet is lost or going.   

[joopv]

Thanks, 

I would have to reproduce the issue then, and with that make work impossible for 300+ employees.  That's not an option.

I had hoped someone would step in with similar experiences and explanation for the same circumstances en enviroment.

Thanks anyway for the responses