Hello, everyone!
Today, I will continue to explain the DHCP protocol. In this second article, I will explain special DHCP messages and lease time.
DHCP messages
If there are some problems with DHCP server or network configuration parameters, we can see the next messages:
DHCP NAK. The DHCP server sends this message to the DHCP client, to indicate to the DHCP client that the time of the leased network parameters has expired or that the requested IP address cannot be assigned. After this step, the DHCP client restarts the process from the beginning.
DHCP DECLINE. The DHCP client sends this message to the DHCP server to tell him that the IP address is already in use. Then the DHCP process starts again.
DHCP RELEASE. When a DHCP client doesn`t want to use the assigned IP address, it sends this message to the DHCP server.
DHCP INFORM. When a DHCP client only has a manually configured IP address and needs other network configuration parameters. The DHCP client then sends this message to the DHCP server.
Lease time
The DHCP server leases the IP address to the DHCP client for a specified period of time. That time is called lease time. The DHCP client can request an extension of the IP address (renewal process).
After the 50% lease time expires, the DHCP client starts the RENEWAL process. The DHCP client sends a unicast DHCP REQUEST RENEWAL to the DHCP server. In this way, the DHCP client requests an extension of the use of network parameters.
If the DHCP server is unavailable, the DHCP client will constantly send a unicast DHCP REQUEST message until it enters the REBINDING state. REBINDING TIMER is usually 85% lease time.
The DHCP client then begins sending a broadcast DHCP REQUEST message to receive a response from any available DHCP server. The available DHCP server can accept (DHCP ACK) or reject the request (DHCP NAK).
In this second article about DHCP, I explained special messages and lease time. If you want to continue reading about DHCP, click on my next link. In the next article Basics of DHCP(3), I will show you DHCP relay principles.
Thank you!
