Hello,
I have a weird issue with IP desk phones and while meraki actually seems to be the fix, I need to understand why.
So we have two Avaya Core switches that each have DHCP relay to 2 remote DHCP servers configured in a failover pair.
Connecting to the cores are a avaya edge switch and a meraki edge switch.
Voice vlan configured on the phone ports is 600.
The ip lease time configured on the server is 8 days.
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When the IP phone connects via the Meraki - it works without a problem.
But when I connect it via the avaya, it connects and I can navigate to its config page, it can call out and be called BUT it goes to get a new IP every 30 seconds or so, and every time it does that there is a slight packet drop that kills any call.
Looking at the DHCP offer packet the phone receives in both cases, from the meraki the IP lease time option is 8 days as expected, but on Avaya its 5 min.
The DHCP failover "max client lead time" is set to 5 min and in the DHCP lease list, I can see that the phone is indeed getting leases of 5 min at a time.
As i understand it, it would only get this 5 min time if there DHCP servers couldn't talk to each other - but its all fine if the phone connects via the meraki switch 😕 (we tried rebooting both servers just for good measure - no effect)
Not that this would rly explain it, as the reconnections are every 30 seconds, not 5 min.
Also, when the reconnects happen, I can see in the packet trace that the phone is actually sending DHCP release messages to the server, so it seems like its the phone that keeps throwing away its IP - but then why doesnt it do it when its connected to a meraki switch?
Something else I noticed looking at packet captures - the phone has Cisco CDP enabled. When connected to meraki, its advertising voip voice vlan as 512.
When connected to Avaya it still sends CDP message but it doesnt include any voice vlan parameter at all.
Since the voice VLAN on the meraki switch port is set to 600, will the meraki switch just ignore the VLAN the phone is advertising in this CDP?
One more thing to make it more incomprehensible - this issue is effecting all desk phones across multiple geographically distant sites. Some sites use the same DHCP server pair that we do, some sites use a different DHCP server pair.
On all sites, if the phones use a meraki switch they are fine, but break on avaya ones.
Oooh, ooh and ANOTHER weird thing - we used to use FUZE as the phone service provider - didn't have this problem. We have just moved to ZOOM and that's when the problem started.
has anyone got any clues that might explain this odd situation? - might it be something do with spanning tree?
Thanks,
