Command " no ip directed-broadcast" ?

Question

I configured a router interface E0 with command"ip address x.x.x.x y.y.y.y" only, but when I "show run", i found there's an extra command under E0(see below) which is "no ip directed-broadcast". I can't remove this line, not sure what this line is doing.
interface Ethernet0
description : connect to O6LXC29OOBC01(switch)
ip address x.x.x.x y.y.y.y
no ip directed-broadcast

Answer 1

Wayne
Jon has provided a good discussion of ip directed-broadcast and the reasons why many people want to disable this. I would like to add a small supplement to his explanation about why it is in the config.
The command is added to the configuration by the IOS. As you comment you did not type it in but it is in the config automatically. A little background may help explain why IOS does automatically put this command into the config.
In earlier versions of IOS the default was to enable directed broadcasts (and in general people thought that it was a good feature). But as networks grew and as we faced more threats and network attacks people began to recognize the security weakness of directed-broadcast and began to want to turn it off. And at some point Cisco changed the default. Now the default is no ip directed-broadcast. And Cisco now automatically adds that to the configuration to be clear about what the behavior of the router will be.
Cisco has done this kind of thing for several commands where the default behavior has changed - to automatically insert into the config the command for the default that has changed (for example putting subnet-zero into the config).
If you want to remove the command no ip directed-broadcast from the configuration you can put ip directed-broadcast into the interface configuration and it will remove the no ip directed-broadcast. (of course it will insert the ip directed-broadcast under the interface configuration)
HTH
Rick