A DHCP Server is
a network server that automatically distributes and assigns:
- IP addresses
- Subnet Mask
- Default Gateway (router)
- DNS Server
A DHCP server relies on the standard protocol DHCP to respond to broadcast queries by clients.
The DHCP employs a connectionless service protocol UDP (User Datagram Protocol) and uses 2 UDP ports: 67 and 68. Port 67 is for a DHCP client (a destination port of a server), and port 68 is for a DHCP server (a destination port of a client). UDP is used instead of TCP because TCP does not support broadcasting, and 2 of the total DHCP messages use broadcasting (DISCOVER and REQUEST).
The DHCP process of assigning
an IP address to a new device on
a network consists of 4 steps which are executed by the following
messages:
- Discovery (DHCPDISCOVER)
- Offer (DHCPOFFER)
- Request (DHCPREQUEST)
- Acknowledgment (DHCPACK)
The list of all DHCP message types is as follows:
| DHCP Message | Purpose |
|---|---|
| DHCPDISCOVER | Client broadcasts to locate available servers. |
| DHCPOFFER | Server offers client configuration parameters. |
| DHCPREQUEST | Client broadcasts requesting offered parameters. |
| DHCPACK | Server responds client confirming a request. |
| DHCPNAK | Client notifies server that IP address is in use. |
| DHCPDECLINE | Server responds client denying a request. |
| DHCPRELEASE | Client requests from server to relinquish an IP address. |
| DHCPINFORM | Client requests configuration parameters from server. |
For detailed explanation of the process, see the “Illustration of DHCP Process with Wireshark” section.
The topology for DHCP Configuration is as follows:
Figure 1. DHCP - Topology 1
Figure 2. DHCP - Topology 2
