What is DHCP ?
- DHCP stands for Dynamic Host Configuration Protocol.
- This is an Application Layer protocol.
- It is use to provide IP address, subnet mask, default Gateway, DNS server address.
- Lease time and DHCP server address to different client nodes in a network.
DHCP works in networking
- DHCPDISCOVER: Broadcast by a client to find available DHCP servers.
- DHCPOFFER: Response from a server to a DHCPDISCOVER and offering IP address and other parameter.
- DHCPREQUEST: Message from a client to servers that does one of the following :-
- Requests the parameters offered by one of the servers and declines all other offers.
- Verifies a previously allocated address after a system or network change (a reboot for example).
- Requests the extension of a lease on a particular address.
- DHCPACK: Acknowledgement from server to client with parameters, including IP address.
- DHCPNACK: Negative acknowledgement from server to client, indicating that the client’s lease has expired or that a requested IP address is incorrect.
- DHCPDECLINE: Message from client to server indicating that the offered address is already in use.
- DHCPRELEASE: Message from client to server canceling remainder of a lease and relinquishing network address.
- DHCPINFORM: Message from a client that already has an IP address (manually configured for example), requesting further configuration parameters from the DHCP server.
Client Server Interactions
- The client broadcasts a DHCPDISCOVER message on its local physical subnet.
- The DHCPDISCOVER message may include some options such as network address suggestion or lease duration.
- Each server may respond with a DHCPOFFER message that includes an available network address (your IP address) and other configuration options.
- The servers record the address as offered to the client to prevent the same address being offered to other clients in the event of further DHCPDISCOVER messages being received before the first client has completed its configuration.
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