Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Command precedence ip helper-address ip directed-broadcast

Of the two commands ip helper-address ip directed-broadcast, which takes precedence when a broadcast arrives?


Posted by WebUser Lance Macdonald from Cisco Support Community App


Re: Command precedence ip helper-address ip directed-broadcast

I think there is not really any precedence.

The usage guidelines of the ip helper-address command states:

The following conditions must be met for a UDP or IP packet to be able to use the ip helper-address command:

The MAC address of the received frame must be all-ones broadcast address (ffff.ffff.ffff).

The IP destination address must be one of the following: all-ones broadcast (, subnet broadcast for the receiving interface (...)

That means that the ip helper has no effect when a directed broadcast is received from another subnet; it has to be a layer-2 broadcast from the local subnet.

If you enable directed broadcasts and send a UDP packet to the subnet's broadcast address as a layer-2 broadcast frame and UDP forwarding is enabled for the port I'd assume that

- an ip unicast packet is send to the configured helper

- an all-ones broadcast is send within the local subnet

Best regards


Btw: Why did you post that in the Data Center - Application Networking section?

CreatePlease to create content