Users Guide

Layer 3 Routing Commands 1485
netbios-dgm (port 138), netbios-ns (port 137), ntp (port 123), pim-auto-
rp (port 496), rip (port 520), tacacs (port 49), tftp (port 69), and time
(port 37). Other ports must be specified by number.
Default Configuration
No helper addresses are configured.
Command Mode
Interface Configuration (VLAN) mode.
User Guidelines
This command can be invoked multiple times on routing interface, either to
specify multiple server addresses for a given port number or to specify
multiple port numbers handled by a specific server. Broadcast packets other
than DHCP require configuration of a destination UDP port number for IP
helper if not listed in Table 6-1. The switch is able to supply the appropriate
UDP destination port numbers by examining the DHCP message, so
configuration of a UDP destination port is not required for unicast forwarding
of DHCP.
The command no ip helper-address with no arguments clears all helper
addresses on the interface.
Example
To relay DHCP packets received on vlan 5 to two DHCP servers, 192.168.10.1
and 192.168.20.1, use the following commands:
console#config
console(config)#interface vlan 5
console(config-if-vlan5)#ip helper-address 192.168.10.1 dhcp
console(config-if-vlan5)#ip helper-address 192.168.20.1 dhcp
To relay both DHCP and DNS packets to 192.168.30.1, use the following
commands:
console#config
console(config)#interface vlan 5
console(config-if-vlan5)#ip helper-address 192.168.30.1 dhcp
console(config-if-vlan5)#ip helper-address 192.168.30.1 domain