DHCP decline message
When a DHCP client receives its IP address from a DHCP server, it should perform a check on the suggested address to ensure that the address is not already in use. For example, the client may issue an ARP request for the IP address. When it does so, the client must fill in its own hardware address as the sender's hardware address, and 0 as the sender's IP address, to avoid confusing ARP caches in other hosts on the same subnet. If the network address appears to be in use, the client MUST send a DHCPDECLINE message to the server. The client SHOULD broadcast an ARP reply to announce the client's new IP address and clear any outdated ARP cache entries in hosts on the client's subnet.
Once this is done, the client will begin theDHCP DORA process from scratch.
If a DHCP server receives a DHCPDECLINE message, the client has discovered through some other means that the suggested network address is already in use. The server MUST mark the network address as not available and SHOULD notify the local system administrator of a possible configuration problem.