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CHAPTER
13-1
Cisco ASDM User Guide
OL-16647-01
13
DHCP, DNS and WCCP Services
A DHCP server provides network configuration parameters, such as IP addresses, to DHCP clients. The
security appliance can provide DHCP server or DHCP relay services to DHCP clients attached to
security appliance interfaces. The DHCP server provides network configuration parameters directly to
DHCP clients. DHCP relay passes DHCP requests received on one interface to an external DHCP server
located behind a different interface.
The Domain Name System (DNS) is the system in the Internet that maps names of objects (usually
hostnames) into IP numbers or other resource record values. The namespace of the Internet is divided
into domains, and the responsibility for managing names within each domain is delegated, typically to
systems within each domain. DNS client services allows you to specify DNS servers to which the
security appliance sends DNS requests, request timeout period, and other parameters.
Dynamic DNS (DDNS) update integrates DNS with DHCP. The two protocols are complementary:
DHCP centralizes and automates IP address allocation; DDNS update automatically records the
association between assigned addresses and hostnames at pre-defined intervals. DDNS allows frequently
changing address-hostname associations to be updated frequently. Mobile hosts, for example, can then
move freely on a network without user or administrator intervention.
For information about configuring these services, see the following sections:
• DHCP Relay
• DHCP Server
• DNS Client
• Dynamic DNS
• WCCP
DHCP Relay
The DHCP Relay pane lets you configure DHCP relay services on the security appliance. DHCP relay
passes DHCP requests received on one interface to an external DHCP server located behind a different
interface. To configure DHCP relay, you need to specify at least one DHCP relay global server and then
enable a DHCP relay agent on the interface receiving DHCP requests.
Restrictions
• You cannot enable a DHCP relay agent on an interface that has a DHCP relay global server
configured for it.
• The DHCP relay agent works only with external DHCP servers; it will not forward DHCP requests
to a security appliance interface configured as a DHCP server.