Network Administration: Understanding DHCP
Dynamic Host Configuration Protocol (DHCP) automatically configures the IP address for every host on a network, thus assuring that each host has a valid, unique IP address. DHCP even automatically reconfigures IP addresses as hosts come and go. As you can imagine, DHCP can save a network administrator many hours of tedious configuration work.
DHCP allows individual computers on a TCP/IP network to obtain their configuration information — in particular, their IP address — from a server. The DHCP server keeps track of which IP addresses are already assigned so that when a computer requests an IP address, the DHCP server offers it an IP address that’s not already in use.
Configuration information provided by DHCP
Although the primary job of DHCP is to dole out IP addresses and subnet masks, DHCP actually provides more configuration information than just the IP address to its clients. The additional configuration information are DHCP options. The following is a list of some common DHCP options that can be configured by the server:
The router address, also known as the Default Gateway address
The expiration time for the configuration information
Domain Name Server (DNS) server address
Windows Internet Name Service (WINS) server address
A DHCP server can be a server computer located on the TCP/IP network. All modern server operating systems have a built-in DHCP server. To set up DHCP on a network server, all you have to do is enable the server’s DHCP function and configure its settings.
A server computer running DHCP doesn’t have to be devoted entirely to DHCP unless the network is very large. For most networks, a file server can share duty as a DHCP server. This is especially true if you provide long leases for your IP addresses.
Many multifunction routers also have built-in DHCP servers. If you don’t want to burden one of your network servers with the DHCP function, you can enable the router’s built-in DHCP server.
An advantage of allowing the router to be your network’s DHCP server is that you rarely need to power-down a router. In contrast, you occasionally need to restart or power-down a file server to perform system maintenance, apply upgrades, or perform troubleshooting.
Most networks require only one DHCP server. Setting up two or more servers on the same network requires that you carefully coordinate the IP address ranges (known as scopes) for which each server is responsible.
If you accidentally set up two DHCP servers for the same scope, you may end up with duplicate address assignments if the servers attempt to assign the same IP address to two different hosts. To prevent this from happening, just set up one DHCP server unless your network is so large that one server can’t handle the workload.