A DHCP NAK is a negative acknowledgment from the DHCP server. The server will send a DHCP NAK in the following scenarios:
- Requested address from possibly the same subnet but not in the address pool of the server. This can be the failover scenario in which 2 DHCP servers are serving the same subnet so that when one goes down, the other should not NAK to clients which got an IP from the first server.
- Requested address is on a different subnet.
- Requested address is already in use by another client.