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2.8 | ![]() |
Helper Addresses | |
2.8.3 | ![]() |
IP helper address example |
Consider this complex sample helper
address configuration.
![]() To configure RTA e0, the interface that receives the Host A broadcasts, to relay DHCP broadcasts as a unicast to the DHCP server, use the following commands:
With this simple configuration, Host A broadcasts using any of the eight default UDP ports will be relayed to the IP address of the DHCP server. However, what if Host A also needs to use the services of the NetBIOS server at 172.24.1.5? As configured, RTA will forward NetBIOS broadcasts from Host A to the DHCP server. Moreover, if Host A sends a broadcast TFTP packet, RTA will also forward this to the DHCP server at 172.24.1.9. What is needed in this example is a helper address configuration that relays broadcasts to all servers on the segment. The following commands configure a directed broadcast to the IP subnet that is being used as a server farm:
Configuring a directed broadcast to the server segment, 172.24.1.255, is more efficient than entering the IP address of every server that could potentially respond to the Host A UDP broadcasts. Finally, some devices on the Host A segment need to broadcast to the TACACS server, which does not reside in the server farm. Configure the RTA e0 to make it work by adding the command ip helper-address 172.16.1.2.Verify the correct helper configuration with the show ip interface command.![]() Notice that the RTA interface e3, which connects to the server farm, is
not configured with helper addresses.
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