Cisco IOS in a Nutshell, 2nd Edition

Name

ip forward-protocol — global

Synopsis

ip forward-protocol {udp [port] | any-local-broadcast | spanning-tree |
turbo-flood}
no ip forward-protocol

Configures

Forwarding of broadcast packets for certain services

Default

Enabled with the ip helper-address command

Description

When the ip helper-address command is configured for an interface, the router “helps” hosts find certain UDP services by forwarding the packets. These services are BOOTP (DHCP), DNS, TFTP, TACACS, TIME, and NetBIOS name and datagram servers. This command allows you to define additional UDP ports that you want forwarded automatically to the helper IP address.

port

Optional. Without this parameter, all the default UDP ports listed here are forwarded. This keyword allows you to forward a specific port. You can disable a default port with the no version of this command.

any-local-broadcast

Forwards any broadcasts including local subnet broadcasts.

spanning-tree

Forwards IP broadcasts that meet the following criteria: First, it must be a MAC level broadcast; second, it must be an IP level broadcast; and third, it must be TFTP, DNS, NetBIOS, ND, TIME, BOOTP, or any other UDP packet specified by an ip forward-protocol udp command.

turbo-flood

Speeds up the flooding of UDP datagrams when using the spanning-tree algorithm. This command should be used in conjunction with the ip forward-protocol spanning-tree command.

Example

To forward port 21000 for a specific application:

ip forward-protocol udp 21000