Administrator Guide

Layer 3 Routing Commands 1541
This command takes precedence over an ip helper-address command given in
global configuration mode. With the following configuration, the relay agent
relays DHCP packets received on any interface other than VLAN 5 and VLAN
6 to 192.168.40.1, relays DHCP and DNS packets received on VLAN 5 to
192.168.40.2, relays SNMP traps (port 162) received on interface VLAN 6 to
192.168.23.1, and drops DHCP packets received on VLAN 6:
console#config
console(config)#ip helper-address 192.168.40.1 dhcp
console(config)#interface vlan 5
console(config-if-vlan5)#ip helper-address 192.168.40.2 dhcp
console(config-if-vlan5)#ip helper-address 192.168.40.2 domain
console(config-if-vlan5)#exit
console(config)#interface 2/6
console(config-if-vlan6)#ip helper-address 192.168.23.1 162
console(config-if-vlan6)#ip helper-address discard dhcp
ip helper enable
Use the ip helper enable command to enable relay of UDP packets. To
disable relay of all UDP packets, use the “no” form of this command.
Syntax
ip helper enable
no ip helper enable
Default Configuration
IP helper is enabled by default.
Command Mode
Global Configuration mode, Virtual Router Configuration mode
User Guidelines
This command can be used to temporarily disable IP helper without deleting
all IP helper addresses.
This command replaces the bootpdhcprelay enable command, but affects not
only relay of DHCP packets, but also relay of any other protocols for which an
IP helper address has been configured.
2CSNXXX_SWUM204.book Page 1541 Monday, January 25, 2016 1:25 PM