Administrator Guide

Layer 3 Routing Commands 1540
• discard — Matching packets should be discarded rather than relayed, even
if a global ip helper-address configuration matches the packet.
•
dest-udp-port — A destination UDP port number from 0 to 65535.
•
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),
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.
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 dns
2CSNXXX_SWUM204.book Page 1540 Monday, January 25, 2016 1:25 PM