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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.

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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