DHCP Client Reuse of an IP Address
If a DHCP client reconnects to a network, it may be able to reuse an IP address that has been previously allocated to it. If a DHCP relay agent is deployed, the DHCP relay agent processes DHCP messages. For more details, see DHCP Server Allocating Network Parameters to New DHCP Clients.
Not all clients can reuse IP addresses that have been allocated to them.
A DHCP client exchanges DHCP messages with a DHCP server, as shown in Figure 1. The DHCP client can obtain network parameters including IP addresses that has been allocated to it after two stages.
The DHCP client broadcasts a DHCP Request message carrying the IP address that the client has previously used. The requested IP address is added in the Option 50 field.
After receiving the DHCP Request message, the DHCP server checks whether there is a lease record based on the MAC address in the message. If there is a lease record matching the MAC address, the DHCP server replies with a DHCP ACK message to notify the DHCP client that the requested IP address can be used. Otherwise, the DHCP server performs no operation and waits for a new DHCP Discover message from the client.