Administrator Guide

Layer 3 Routing Commands 1477

User Guidelines

Enable DHCP Relay using the ip helper enable command. The interface

configuration always takes precedence over global configuration. However, if

there is no interface configuration, then global configuration is followed. Use

the ip dhcp relay information option command to globally enable inclusion

of Option 82 information in DHCP requests forwarded to a DHCP server.

Example

The following example enables the circuit ID and remote agent ID options on

VLAN 10.

console(config)#interface vlan 10

console(config-if-vlan10)#ip dhcp relay information option-insert

ip helper-address (global configuration)

Use the ip helper-address (global configuration) command to configure the

relay of certain UDP broadcast packets received on any interface. To delete an

IP helper entry, use the no form of this command.

Syntax

ip helper-address server-address [dest-udp-port | dhcp | domain | isakmp |

| tacacs | tftp | time]

no ip helper-address [server-address] [dest-udp-port | dhcp | domain |

auto-rp | rip | tacacs | tftp | time]

• server-address — The IPv4 unicast or directed broadcast address to which

relayed UDP broadcast packets are sent. The server address cannot be an

IP address configured on any interface of the local router.

• dest-udp-port — A destination UDP port number from 1 to 65535. This

parameter need not be configured for DHCP. It must be configured for all

other protocols which are to be relayed.

• port-name — The destination UDP port may be optionally specified by its

name. Whether a port is specified by its number or its name has no effect

on behavior. The names recognized are as follows: dhcp (port 67), domain

(port 53), isakmp (port 500), mobile-ip (port 434), nameserver (port 42),