102 Routing ConfigurationThe relay agent only relays packets that meet the following conditions:• The destination MAC address must be the all-ones broadcast address (FF:FF:FF:FF:FF:FF).• The destination IP address must be the limited broadcast address (255.255.255.255) or a directedbroadcast address for the receive interface.• The IP time-to-live (TTL) must be greater than 1.• The protocol field in the IP header must be UDP (17).• The destination UDP port must match a configured relay entry.CLI ExamplesExample 1: Enable/Disable IP HelperTo globally enable/disable IP Helper (relay of UDP packets) use the following command:console (config)#ip helper enableExample 2: Configure IP Helper Globally (DHCP)To relay DHCP packets received on any interface to two DHCP servers (10.1.1.1 and 10.1.2.1), use thefollowing commands:console (config)#ip helper-address 10.1.1.1 dhcpconsole (config)#ip helper-address 10.1.2.1 dhcpExample 3: Enable IP Helper Globally (UDP)To relay UDP packets received on any interface for all default ports (Table 2) to the server at 20.1.1.1, usethe following commands:console (config)#ip helper-address 20.1.1.1Example 4: Enable IP Helper on a VLAN Routing Interface to a Server (DHCP)To relay DHCP packets received on VLAN 100 to two DHCP servers, 192.168.10.1 and 192.168.20.1, usethe following commands:console(config)#interface vlan 100console(config-if-vlan100)#ip helper-address 192.168.10.1 dhcpconsole(config-if-vlan100)#ip helper-address 192.168.20.1 dhcp
