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

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member


what is the purpose of the command "no ip directed-broadcast"? Would this command prevent the router from passing udp packets?

New Member

Re: directed-broadcast

This is related to helper addresses. With those, you can specify a particular host or an entire subnet as a target. If you elect to forward to the entire subnet, you need to enable 'ip directed-broadcast' on the target subnet ethernet interface. They are by default not allowed because of DoS concerns.

To answer a little more directly, this has no impact on the *routing* of udp packets. Just affects what happens when certain types of relayed broacasts are received on an interface.

New Member

Re: directed-broadcast

To elaborate on the possibilities, there are cases where no ip directed broadcast on a LAN can impact the receipt of an UDP-based application. I have seen some legacy "ticker-type" applications (UDP-based) that rely on the IP directed broadcast feature to broadcast UDP packets to clients on selected subnets.

For example, a "ticker-type" application server may have a list of subnets such as and where the clients of the application reside. It sends ticker updates to and If IP directed broadcast is not enabled on the interfaces hosting these subnets, the ticker clients will not receive the traffic from the application.

CreatePlease login to create content