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DoS Step-by-Step: Controlling Directed Broadcasts (From

Revision: 1.9 - Date: 2006/05/10 15:38:39 GMT

For Cisco routers the following command needs to be set on each interface on each router.

no ip directed-broadcast

The no ip directed-broadcast command is the default in Cisco IOS software version 12.0 and later. For earlier versions you will need to follow the steps below.

To turn off directed broadcasts you will need to set "no ip directed-broadcast" on each interface on the router that has an ip address. To find out the interfaces use "the show ip interface brief" command. Then you will go to each interface and issue the "no ip directed-broadcast" command.

router# show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
Ethernet0         YES NVRAM  up                    up
Serial0                unassigned      YES unset  up                    up
Serial0.1         YES unset  up                    up
Serial1                unassigned      YES unset  up                    up

router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
router(config)# interface Ethernet0
router(config-if)# no ip directed-broadcast
router(config-if)# interface Serial0.1
router(config-subif)# no ip directed-broadcast
router# write
Building configuration...