Host Configuration
Internet hosts need to be configured with certain information
that allows applications to operate and packets to be routed. Information that
is most commonly configured includes the IP address, the gateway, and the DNS
server. Configuration can be done manually or can be via an automated process.
Manual configuration requires the user to be networking savvy to some extent.
The Dynamic Host Configuration Protocol (DHCP) provides configuration parameters
to Internet hosts. DHCP is specified in RFC 2131. DHCP is an
application-layer protocol that follows the client/server mode. From the client
perspective, it can be viewed as an extension to BOOTP, which is used to
bootstrap hosts. One thing to note about DHCP is that it is for confguring hosts
only and is not intended for routers.
There are primarily two components to DHCP: a client piece of
software and a DHCP server. After obtaining parameters via DHCP, a DHCP client
should be able to exchange packets with any other host in the Internet. The main
services provided by DHCP are to provide persistent storage of network
parameters for network clients and to allocate temporary or permanent network
(IP) addresses to clients. IP address allocation in DHCP has three
mechanisms:
-
Automatic— A permanent IP
address is assigned to the client.
-
Dynamic— An IP address is
allocated to the client with a lifetime associated with it.
-
Manual— The IP address is
assigned by the operator and DHCP is simply the carrier of this
information.
Other extensions to DHCP include the concept of a relay agent
that can forward DHCP messages to a server that is located elsewhere in the
network. Clients broadcast a DHCPDISCOVER message on the local physical subnet
and servers on the network respond with a DHCPOFFER message. The client selects
one of the offers and sends a DHCPREQUEST message to the server that made the
offer. The server responds with a DHCPACK, and initialization is complete
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