Dear,

By default, IP directed broadcasts are dropped; they are not forwarded. By dropping IP directed broadcasts, routers are less susceptible to denial-of-service attacks.

You can enable forwarding of IP directed broadcasts on an interface where the broadcast becomes a physical broadcast. If such forwarding is enabled, only those protocols configured using the ip forward-protocol global configuration command are forwarded.

You can specify an access list to control which broadcasts are forwarded. When an access list is specified, only those IP packets permitted by the access list are eligible to be translated from directed broadcasts to physical broadcasts.

You will found full details about that in the below URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_c/1cprt2/1cipadr.htm

Please Rate helpful posts.

Best Regards,

Mounir Mohamed