We had a ShoreTel SG90BRI switch that was brand new and failed to boot. It always tried to request a DHCP address and it looked like it get's no answer from DHCP first. This was wrong as the network is clean and working properly. It is just the operating system of ShoreTel that is broken and not updating it's DHCP settings after moving the switch from one network to another.
Symptom:
The switch boots up and shows you this in an endless loop:
Searching for active link
Found active link on port 1
ENET Speed is 100 Mbps - FULL duplex connection
DHCP broadcast 1
DHCP broadcast 2
DHCP broadcast 3
DHCP broadcast 4
DHCP broadcast 5
