We have a customer that recently upgraded some of their Meraki switches to 15.21.1. After doing so, they started to notice issues with DHCP (external server, no Meraki-run DHCP) and devices only getting 169.254.x.x self-assigned IP addresses. Checking the uplink switch that this switch connects to, we ran packet captures on the uplink port that feeds the problematic switch. We noticed DHCP Discovers and Requests, no Offers or Acknowledgements coming to and through the port. Also, the event log showed a ton of DHCP blocked messages. Digging further, we also saw UDLD alerts on this port, and the link negotiating at 100 Mbps instead of 1 Gbps. I learned at this point that the uplink switch and problem switch are connected via a wireless bridge that uses a Ubiquiti wireless device on each end. Back on the switch in question, one of the AP's connected to it appears to be getting assigned dozens and dozens of IP addresses from within the DHCP pool, which is probably why there's a lot of DHCP blocked messages on the uplink side. The customer states that this issue was non-existent before the upgrade. The main troubleshooting step we have tried thus far is to have them move the problem AP and the problem switch over to the same location as the uplink switch, and instead of connecting over wireless bridge, connect physically direct. Once this was done, all problems vanished. DHCP worked fine and there were no further disruptions. While it seems like the wireless bridge is the problem, the customer is frustrated by the fact that it worked just fine prior to the code upgrade. In addition, he's now saying there are other switches in their network that are running on that code and experiencing "intermittent" connectivity issues as well. Has anyone else encountered these issues and do you think the focus should be on the firmware? Any suggestions welcome as this is a weird one.
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