Relay DHCP broadcasts as a unicast to the DHCP server, use the followingĬommands: RTA(config)#interface e0 RTA(config-if)#ip helper-address 172.24.1.9 To configure RTA e0, the interface that receives the Host A broadcasts, to Because RTA will not forward the Host A DHCPDISCOVERīroadcast, RTA must be configured to help Host A. You want Host A to automatically obtain its IP configuration from the DHCP RTA(config-if)#ip helper-address 192.168.1.254 RTA(config-if)#exit RTA(config)#ip forward-protocol udp 517 RTA(config)#no ip forward-protocol udp 37 RTA(config)#no ip forward-protocol udp 49 RTA(config)#no ip forward-protocol udp 137 RTA(config)#no ip forward-protocol udp 138 IP Helper Address ExampleĬonsider the complex sample helper address configuration shown in FigureĢ-22. That the router be configured according to the syntax shown in Example Without forwarding Time, TACACS, and NetBIOS, the Cisco IOS software requires Not only to add a UDP port to the default eight, but also to subtract an To forward UDP on port 517, use the globalĬonfiguration command ip forward-protocol udp 517. Ip forward-protocol to allow an administrator to forward any UDP port inĪddition to the default eight. On this list? The Cisco IOS software provides the global configuration command What if Company XYZ needs to forward requests for a service not The ip helper-address command to define the address to which UDPīroadcasts for services should be forwarded.īy default, the ip helper-address command forwards the eight UDP To configure the helper address, identify the router interface that will Alternatively, the router canįorward these requests as directed broadcasts to a specific network or Helper-address command to relay broadcast requests for these key Userīy using the ip helper-address command, a router can be configured toĪccept a broadcast request for a UDP service and then forward it as a unicast toĪ specific IP address, as shown in Figure 2-21. Running services such as DHCP or DNS on severalĬomputers creates overhead and administrative problems, so the first option is Must provide DHCP and DNS servers on all subnets or use the Cisco IOS software Some clients are unable to make aĬonnection without services such as DHCP. Such remoteĬlients broadcast to locate these servers, but routers, by default, do notįorward client broadcasts beyond their subnet. Network, clients might not reside on the same subnet as key servers. Need to broadcast to locate a TACACS security server. Other devices might use broadcasts to locate TFTP servers. ![]() This sectionĭescribes some of the purposes of and scenarios in which to use helperĭHCP is not the only critical service that uses broadcasts. This section describes how networks and routers use helper addresses toįorward broadcasts to another server or router on another network.
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