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IP helper-address Explained

All broadcasts messages are dropped by the router when it receives on an interface. This specific command is enables the router to convert the broadcast messages distended for a specific destination into unicast. This interface level command needs to be applied on the interface which the broadcast receives from.

R1(config-if)#ip helper-address

Also there are other options where you point the address to a vrf etc…

The following broadcasts are forwarded by default…

TIME – Port 37
TACACS – Port 49
DNS – Port 53
BOOTP/DHCP Server – Port 67
BOOTP/DHCP Client – Port 68
TFTP – Port 69
NetBIOS Name Service – Port 137
NetBios Datagram Service – Port 138

Other protocols can be forwarded by using the following Global config commanding…

R1(config)#ip forward-protocol udp ?

Use the ? to see the supported protocols. You may use the following command to remove a specific protocol being forwarded…

R1(config)#no ip forward-protocol udp ?
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