218 BigIron RX Series Configuration Guide53-1002253-01Configuring forwarding parameters7• tftp (port 69)In addition, you can specify any UDP application by using the application’s UDP port number.The parameter specifies the UDP application port number. If the application youwant to enable is not listed above, enter the application port number. You also can list the portnumber for any of the applications listed above.To disable forwarding for an application, enter a command such as the following.BigIron RX(config)# no ip forward-protocol udp snmpSyntax: [no] ip forward-protocol udp snmpThis command disables forwarding of SNMP requests to the helper addresses configured on deviceinterfaces.Configuring an IP helper addressTo forward a client’s broadcast request for a UDP application when the client and server are ondifferent networks, you must configure a helper address on the interface connected to the client.Specify the server’s IP address or the subnet directed broadcast address of the IP subnet theserver is in as the helper address.You can configure up to 16 helper addresses on each interface. You can configure a helperaddress on an Ethernet port or a virtual interface.To configure a helper address on interface 2 on device module 1, enter the following commands.BigIron RX(config)# interface e 1/2BigIron RX(config-if-e1000-1/2)# ip helper-address 207.95.7.6The commands in this example change the CLI to the configuration level for port 1/2, then add ahelper address for server 207.95.7.6 to the port. If the port receives a client request for any of theapplications that the device is enabled to forward, the device forwards the client’s request to theserver.Syntax: ip helper-address The command specifies the server’s IP address or the subnet directed broadcastaddress of the IP subnet the server is in.Configuring BootP/DHCP forwarding parametersThe DHCP relay will allow for IP address grants that do not match the subnets configured on theinterface that the DHCP request was received. A host on an IP network can use BootP/DHCP toobtain its IP address from a BootP/DHCP server. To obtain the address, the client sends aBootP/DHCP request. The request is a subnet directed broadcast and is addressed to UDP port 67.A limited IP broadcast is addressed to IP address 255.255.255.255 and is not forwarded by thedevice or other IP routers.When the BootP/DHCP client and server are on the same network, the server receives thebroadcast request and replies to the client. However, when the client and server are on differentnetworks, the server does not receive the client’s request, because the device does not forward therequest.
