Dhcp offer disappearing

[Lars_Petterson]

Hi,

We are having problems with our dhcp when connecting it to ms125 switch. We see that the dhcp offer are being processed but somewhere they dissapear and they go through ms125 switch! Has anyone else had the same issue?

[ww]

Make sure  your dhcp server is allowed

https://documentation.meraki.com/MS/Monitoring_and_Reporting/MS_DHCP_Servers#Overview

[Lars_Petterson]

It is allowed on the switch and the dhcp server is an external windows dhcp server. 

[Inderdeep]

@Lars_Petterson : Check these links

https://community.meraki.com/t5/Switching/DHCP-Server-Disappeared/td-p/110837

https://documentation.meraki.com/MR/Monitoring_and_Reporting/DHCP_%22no_offers_received%22_Errors_in... 

[Lars_Petterson]

Thank you for the response. The problem is that we see on the MX that the dhcp offer is present but then somehow they dont reach the client and no clients gets an IP. We have MS125 switches that stands between the clients and the dhcp server. 

[cmr]

@Lars_Petterson several years ago we had a similar issue where the config was as below:

Cisco L3 switch running DHCP server -> Juniper EX2200 switch -> Cisco L2 switch.

The devices on the Cisco L2 switch never received the offers, however if you directly connected the Cisco switches together or were a client on either of the other switches all was well.  We did a complete packet analysis to confirm that it was being dropped on the exit from the Juniper, but found no reason.

Is your setup simply MX -> MS125 or are there any other networking devices in the path?

[Lars_Petterson]

Hi cmr,

I have atached the topology.

The clients connect to a switch (non-meraki switch) and the switch is connected then with fiber to the meraki switch. The links between the MS:es and MX:es are configured as trunks to allow for different vlans. The clients and the DHCP server lies on the same vlan. So it should be all layer 2 traffic without anything disturbing it. The dhcp server is located on the other switch. I have tested to move the dhcp server on the other switch but it was still no dhcp offer reaching the clients and as I said before when doing packet capture on the MX:es we see dhcp replies but still no client gets any IP.

[cmr]

@Lars_Petterson if you connect a client to either of the Meraki switches does it get a DHCP address?  I'd expect a connection between the two switches, is there a reason that you don't have this?  Connecting them via MXs is not a recommended topology.

[Lars_Petterson]

If I connect on the meraki switch where the dhcp server is connected then I do get an IP otherwise dont. I have tested also with a link between the meraki switches but stp blocks the port and the link is disabled. The reason why we have ths topology is because we want to have some redudance. Do you have any other proposal on how we could re-arrange the links?

[cmr]

• Connect a cable between the switches and set both ports to trunk all VLANs
• Disable the port on switch 1 that links to MX 2
• Disable the port on switch 2 that links to MX 1

As you make each change you may get an interruption of network traffic for up to 30 seconds as spamming tree sorts itself out, so try to do out of hours or at a quiet time.

Once completed then test if a client gets DHCP when connected to:

• Same switch as DHCP server
• Other Meraki switch
• Non Meraki switch

[cmr]

The above should read spanning-tree as opposed to spamming tree, but I actually quite like the idea of a spamming tree 😈