Some network nodes utilize the DHCP (Dynamic Host Configuration Protocol) to automatically retrieve their network configurations from a centralized server.
The network configuration information that the DHCP server provides can include items such as:
- DNS server IP addresses
- DNS hostname
- The default router’s IP address
- Broadcast address
- Subnet mask
- ARP cache timeout
- MTU for the interface
- NTP Servers
- SMTP server
- TFTP server
- WINS name server
The DHCP clients’ MAC addresses identify them.
The DHCP protocol utilizes UDP ports 67 and 68, which are the same ports that BOOTP uses.
DHCP Messages
The DHCP protocol consists of eight discrete message types:
| DHCP Message | Description |
|---|---|
| DHCP Discover | UDP broadcast from DHCP client to locate available servers. |
| DHCP Offer | DHCP server to client in response to DHCP Discover with offer of configuration parameters. |
| DHCP Request | Client response to servers either requesting offered parameters from one server and implicitly declining offers from all others, confirming correctness of previously allocated address after, e.g. system reboot, or extending the lease on a particular network address. |
| DHCP ACK | Server to client with configuration parameters, including committed network address. |
| DHCP NAK | Server to client indicating client’s notion of network address is incorrect (e.g. client has moved to new subnet) or client’s lease has expired. |
| DHCP Decline | Error message from DHCP client to server indicating network address is already in use. |
| DHCP Release | Message from DHCP client to server releasing network address and canceling remaining lease. |
| DHCP Inform | Client asking DHCP server only for local configuration parameters because the client already has externally configured network address. |
Additional Reading on DHCP
The DHCP protocol is defined in RFC 2131: Dynamic Host Configuration Protocol.
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Very useful information about DHCP. Thank you!