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208 Chapter 7: Configuring a Cisco 700 Series Router

The 700 IOS DHCP server gives the SOHO administrator a much simpler IP address
management scheme. DHCP enables the small office with the capability to provide IP
addressing on an as-needed basis for each local client. This method eliminates address
management on a PC-by-PC basis, which reduces client configuration tasks and costs. Hosts in
remote offices can obtain dynamic IP addresses directly from the local 700 series router.

DHCP has been generally adopted as the standard for assigning addresses to an internal
network. This frees the administrator from configuring and maintaining an address scheme on
a PC-by-PC basis.

For more information on the inner workings of DHCP, you can turn to the following references
(all of which can be accessed from www.isi.edu/in-notes/):

RFC 951--Bootstrap Protocol (BOOTP)

RFC 1542--Clarifications and Extensions for the Bootstrap Protocol

RFC 2131--Dynamic Host Configuration Protocol

RFC 2132--DHCP Options and BOOTP Vendor Extensions

These RFCs can be a bit heady for understanding the average uses of DHCP. Nonetheless, the
basic thrust of this technology has been widely implemented and accepted. In fact, all Cisco
routers can understand and implement this function per the standards.

Using the Cisco 700 Series Router as a DHCP Server and
Relay Agent

The 700 series router is capable of being the DHCP server or functioning as a relay agent to a
DHCP server running on another device. To perform the function of a relay agent, the router is
configured as follows:

set dhcp relay

ip-address

The use of the 700 series router as a relay agent is very similar to setting an IP helper-address
on an IOS router pointing to a DHCP server. Using the set dhcp relay command passes only
the DHCP request; however, the IP helper-address can pass other broadcast packets if not
configured for only DHCP requests. The use of the router as a relay agent simply points to
another device responsible for the maintenance of the IP addressing.

Using the 700 series router as a DHCP server is also syntactically very simple: the router must
be declared as the server and the address pool must be defined. Any DHCP broadcast request
received from the LAN interface is satisfied from the pool. The code in Example 7-4 is required
on the router shown in Figure 7-4.