23.0 DHCP
The purpose of the dynamic host configuration
protocol (DHCP) is to assign network settings centrally from a
server rather than configuring them locally on each and every
workstation. A host configured to use DHCP does not have control over its
own static address. It is enabled to configure itself completely and
automatically according to directions from the server. If you use the
NetworkManager on the client side, you do not need to configure the client at all.
This is useful if you have changing environments and only one interface
active at a time. Never use NetworkManager on a machine that runs a DHCP server.
One way to configure a DHCP server is to identify each client using the
hardware address of its network card (which should be fixed in most
cases), then supply that client with identical settings each time it
connects to the server. DHCP can also be configured to assign addresses to
each interested client dynamically from an address pool set up for that
purpose. In the latter case, the DHCP server tries to assign the same
address to the client each time it receives a request, even over longer
periods. This works only if the network does not have more clients than
addresses.
DHCP makes life easier for system administrators. Any changes, even bigger
ones, related to addresses and the network configuration in general can be
implemented centrally by editing the server's configuration file. This is
much more convenient than reconfiguring numerous workstations. Also it is
much easier to integrate machines, particularly new machines, into the
network, because they can be given an IP address from the pool. Retrieving
the appropriate network settings from a DHCP server is especially useful
in the case of laptops regularly used in different networks.
In this chapter, the DHCP server will run in the same subnet as the
workstations, 192.168.2.0/24 with 192.168.2.1 as gateway. It has the
fixed IP address 192.168.2.254 and serves two address ranges, 192.168.2.10 to
192.168.2.20 and 192.168.2.100 192.168.2.200;.
A DHCP server supplies not only the IP address and the netmask, but also
the hostname, domain name, gateway, and name server addresses for the
client to use. In addition to that, DHCP allows a number of other
parameters to be configured in a centralized way, for example, a time
server from which clients may poll the current time or even a print
server.
