×

Warning message

  • Cisco Support Forums is in Read Only mode while the site is being migrated.
  • Cisco Support Forums is in Read Only mode while the site is being migrated.
Rolf Fischer Thu, 08/22/2013 - 11:58
User Badges:
  • Blue, 1500 points or more

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 (255.255.255.255), 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

Rolf



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

Actions

This Discussion