Has anyone seen problems with DHCP and VOIP phones. On our local network ALL devices pull DHCP address. One or more of the Polycom phones keep coming up complaining of duplicate IP conflict. Problem moves around between the 5-6 phonesets we have with one or two ALWAYS coming up complaining. Don’t think it is the phones themselves as we purchased a brand new phone (so it would have unique MAC address) and when put on the network it came up, pulled an IP address from DHCP server in IPFire router, and compained that it was conflicting with an existing IP address given out to some other device on the local network.
and was it conflicting.
From the dhcp page you should be able to see what dynamic IP was given and compare that with any fixed leases you have. Also compare what IP the phone says that it has with what the IPFire dhcp page says it was given.
Know that page by heart.
Additional facts, things done, and clues:
–Network consists of 6-8 Win10 workstations, 5 to 6 Polycom phones, and 2 Brother printers).
–This network has been working fine for two to three years until just recently
–Don’t have any other devices that could accidentally act as a DHCP server on the local LAN
–None of the workstations has ever had a conflict, only the phones.
–No new workstations or other devices have been added to the network recently
–No changes to infrastructure wiring, layout, configuration, etc
–Have rebooted the IPFire router a couple of times (just to be sure)
–Since the switch does its thing at MAC address level have tried rebooting it (several times)
–Ensured that the DHCP address pool range is sufficient to cover the number of devices present
–Have studied the MAC addresses carefully and the MAC address of the phone is on the expired leases list where it was previously assigned some other valid IP address, but it now is complaining that the DHCP server has given it an IP that conflicts.
–Did have one phone that was acting up that suddenly went through some kind of firmware upgrade or whatever, ie cycled through several files downloaded, reset itself several times, etc, then came up fine and hasn’t been a problem since. Problem then started popping up on one or two of the other phones.
–Checked with the vendor that all phones are at current firmware/software etc.
–Did factory reset on one of the phones and re-generated the online profile. Didn’t help
–Purchased a new phone, which should have a never seen before MAC to the network to see if it would have the same problem. It does.
–The MAC address of phone and the MAC address of the workstation are different. It seems in fact like a situation where during the handshake, the DHCP server tries to hand out a bad IP address, or the phone thinks that the DHCP server is saying one thing when in reality it is saying something else. Since we have had several core updates in the past year or so,I just thought to ask the original question here.
Would like to turn off everything, then “flush” the entire address pool on the DHCP server (if there was a way to do that), then bring up each device one by one, verify what address it gets, and see where we are. If problem comes back when leases start expiring again I will just pull my hair out and scream. That should certainly help 
Disable the green and blue dhcp sections and press save then re-enable them and press save. The lease cache on the dhcp server will be cleared by the above but you need to disable both blue and green checkboxes.