Configuring Dhcp Relay Services; Dhcp Relay Overview; Configuring The Dhcp Relay Agent - Cisco 7604 Configuration Manual

Chapter 8 Configuring IP Routing and DHCP Services
•

Configuring DHCP Relay Services

This section describes how to configure DHCP relay services provided by the FWSM. This section
includes the following topics:
•
•
•
•

DHCP Relay Overview

You can configure a DHCP relay agent to forward DHCP requests received on an interface to one or more
DHCP servers. When a DHCP request enters an interface, the DHCP servers to which the FWSM relays
the request depends on your configuration. You can configure the following types of servers:
•
•
The following restrictions apply to the use of the DHCP relay agent:
•
•
•
•

Configuring the DHCP Relay Agent

To enable DHCP relay, perform the following steps:
Set the IP addresses of DHCP servers using one or both of the following methods:
Step 1
•
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM
OL-20748-01
The server_ip1 is the IP address or name of the primary TFTP server while server_ip2 is the
IP address or name of the secondary TFTP server. A maximum of two TFTP servers can be
identified using option 150.
To provide set the default route, enter the following command:
hostname(config)# dhcpd option 3 ip router_ip1
DHCP Relay Overview, page 8-39
Configuring the DHCP Relay Agent, page 8-39
Preserving DHCP Option 82, page 8-41
Verifying the DHCP Relay Configuration, page 8-41
Interface-specific DHCP servers—When a request enters a particular interface, then the FWSM
relays the request only to the interface-specific servers.
Global DHCP servers—When a request enters an interface that does not have interface-specific
servers configured, then the FWSM relays the request to all global servers. If the interface has
interface-specific servers, then the global servers are not used.
The relay agent cannot be enabled if the DHCP server feature is also enabled.
DHCP Relay services are not available in transparent firewall mode. You can, however, allow DHCP
traffic through using an access list. To allow DHCP requests and replies through the FWSM in
transparent mode, you need to configure two access lists, one that allows DCHP requests from the
inside interface to the outside, and one that allows the replies from the server in the other direction.
Clients must be directly-connected to the FWSM and cannot send requests through another relay
agent or a router.
For multiple context mode, you cannot enable DHCP relay on an interface that is used by more than
one context.
To configure an interface-specific server, enter the following commands:
hostname(config)# interface {vlan vlan_id | mapped_name}
hostname(config-if)# dhcprelay server ip_address
Configuring DHCP
8-39