Problem with Cisco phones

[Marki]

Hello,

I know this is probably not an ISC DHCPD issue per se, but anyway, maybe 
it rings a bell with someone.

I have a very frustrating issue here with Cisco IP Phones 8800 series.

Some of them are doing REQUEST/ACK multiple times per minute. They are 
doing it as a broadcast, not unicast, hence the relay IP is shown.

2023-03-24T08:53:35.946166+01:00 d01 dhcpd: DHCPREQUEST for 172.17.8.11 
from xx:yy:zz:d9:11:57 (SEP) via 172.17.8.1
2023-03-24T08:53:35.946183+01:00 d01 dhcpd: DHCPACK on 172.17.8.11 to 
xx:yy:zz:d9:11:57 (SEP) via 172.17.8.1

2023-03-24T08:53:43.938781+01:00 d01 dhcpd: DHCPREQUEST for 172.17.8.11 
from xx:yy:zz:d9:11:57 (SEP) via 172.17.8.1
2023-03-24T08:53:43.938798+01:00 d01 dhcpd: DHCPACK on 172.17.8.11 to 
xx:yy:zz:d9:11:57 (SEP) via 172.17.8.1

2023-03-24T08:54:03.943809+01:00 d01 dhcpd: DHCPREQUEST for 172.17.8.11 
from xx:yy:zz:d9:11:57 (SEP) via 172.17.8.1
2023-03-24T08:54:03.943828+01:00 d01 dhcpd: DHCPACK on 172.17.8.11 to 
xx:yy:zz:d9:11:57 (SEP) via 172.17.8.1

Some are even switching between broadcast and unicast:

2023-03-24T08:13:21.774638+01:00 d01 dhcpd: DHCPREQUEST for 172.17.8.31 
from xx:yy:zz:d1:9d:11 (SEP) via 172.17.8.1
2023-03-24T08:13:21.774658+01:00 d01 dhcpd: DHCPACK on 172.17.8.31 to 
xx:yy:zz:d1:9d:11 (SEP) via 172.17.8.1
-- nothing in between --
2023-03-24T09:12:03.817128+01:00 d01 dhcpd: DHCPREQUEST for 172.17.8.31 
from xx:yy:zz:d1:9d:11 (SEP) via vlan50
2023-03-24T09:12:03.817151+01:00 d01 dhcpd: DHCPACK on 172.17.8.31 to 
xx:yy:zz:d1:9d:11 (SEP) via vlan50

Sometimes they are totally stuck for like half an hour. First they 
DISCOVER all the time, but don't issue a REQUEST after the OFFER until 
some time has passed.

Power cycling does not help. I have yet to lay hand on a specimen in 
order to totally reset it.

This could have started with failover not having been configured 
correctly between the two dhcp servers, i.e. both servers handing out 
addresses for dynamic pools.

Anyone got an idea?

Thanks
Marki