Filter
Top Products
Chapter 17. DHCP Server
Dynamic Host Configuration Protocol, or DHCP, provides a framework for passing
configuration information to hosts on a TCP/IP network. DHCP functions either as a
DHCP server or as a BOOTP/DHCP Relay Agent. If DHCP functions as a DHCP
server, it processes DHCP packets on the local system. If DHCP functions as a
BOOTP/DHCP Relay Agent, it relays DHCP and BOOTP packets on the local
system but does not process them. The Relay Agent forwards the packets to one or
more different server IP addresses. The Relay Agent uses port 67, the same port
that the BOOTP or DHCP server uses.
During configuration, you must specify the IP addresses that the Relay Agent uses
for forwarding. When the Relay Agent forwards a packet, it inserts its address into
the packet. It does this so the DHCP or BOOTP server can return a response to
that Relay Agent. For more information on DHCP Relay Agents, see “DHCP Relay
Agent” on page 420.
DHCP Overview
DHCP enables client machines to get network configuration information, including
an Internet Protocol (IP) address, from a central DHCP server. The administrator
sets the DHCP server to assign the network information to each client, which
makes the process transparent to the user. DHCP saves time, reduces errors, and
insures the consistency of the configurations for mobile and non-mobile users.
What is DHCP?
DHCP is a client/server protocol that enables you to centrally locate and
dynamically distribute configuration information, including IP addresses.
DHCP is based on the Bootstrap Protocol, or BOOTP, and adds the capability for
automatically allocating reusable network addresses. It also adds the capability for
distributing additional host configuration options. DHCP clients and servers use
existing BOOTP/DHCP Relay agents.
DHCP defines IP address allocation policies, including the following:
Dynamic
A DHCP server assigns an IP address to a requesting BOOTP or DHCP client
from a range of available addresses.
Static
A DHCP server administrator assigns a static, pre-defined address that is
reserved for a specific BOOTP or DHCP client.
DHCP provides the following lease policies for IP addresses:
Temporary
An IP address is temporarily
leased
to a DHCP client. To continue using the
address, a DHCP client that does not have a permanent lease must periodically
request the renewal of its lease on its current IP address. The process of
renewing leased IP addresses occurs dynamically as part of the DHCP
protocols. It is not generally visible to end users.
© Copyright IBM Corp. 1997, 1999 405