Cisco IP phones unable to reach DHCP server from a particular subnet/vlan.
Posted on 2015-02-17
DHCP server is normally responding to the request made by IP phones residing in all vlans, but when a DHCP request is coming from one particular block of subnets let suppose 192.168.208.1/22 and 192.168.216.1/22 and 192.168.224.1/22, the DHCP is unable to respond or IP phones are failing to reach the dhcp sever.
For reachability we did some pinging from those troubled subnets, pings are reaching easily the DHCP server, placed a laptop in those troubled subnets to check if it was getting an IP address and the laptop did get an IP, but why only phones are are unable to get an IP address and is stuck in "Registering" mode .
Any clue ?