Configuring Dhcp Relay - Cisco Catalyst 6500 Series Configuration Manual

Chapter 8 Configuring IP Addresses, Routing, and DHCP
You can configure the FWSM to send information for most options listed in RFC 2132. The following
table shows the syntax for any option number, as well as the syntax for commonly-used options 66,150,
and 3:
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Configuring DHCP Relay

Routed firewall mode only
A DHCP relay agent allows the FWSM to forward DHCP requests from clients to a router connected to
a different interface.
The following restrictions apply to the use of the DHCP relay agent:
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To enable DHCP relay, follow these steps:
Step 1 To set the IP address of a DHCP server on a different interface from the DHCP client, enter the following
command:
FWSM/contexta(config)# dhcprelay server ip_address
You can use this command up to 10 times to identify up to 10 servers.
To enable DHCP relay on the interface connected to the clients, enter the following command:
Step 2
FWSM/contexta(config)# dhcprelay enable interface
(Optional) To set the number of seconds allowed for relay address negotiation, enter the following
Step 3
command:
FWSM/contexta(config)# dhcprelay timeout seconds
OL-6392-01
To provide information for DHCP requests that include an option number as specified in RFC-2132,
enter the following command:
FWSM/contexta(config)# dhcpd option number string
To provide the IP address or name of a TFTP server for option 66, enter the following command:
FWSM/contexta(config)# dhcpd option 66 ascii server_name
To provide the IP address or names of one or two TFTP servers for option 150, enter the following
command:
FWSM/contexta(config)# dhcpd option 150 ip server_ip1 [ server_ip2 ]
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 a list of router IP addresses for option 3, enter the following command:
FWSM/contexta(config)# dhcpd option 3 ip router_ip1 [ router_ip2 ] [...]
The relay agent cannot be enabled if the DHCP server feature is also enabled.
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 (a shared VLAN).
Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide
Configuring DHCP Relay
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