smurf's attack...

Folks, this is a bad idea. There are lots of completely valid IP
addresses out there that end in .255. True, most of them that
end in .255 ARE broadcast addresses, but if people implement this
kind of filtering on a large scale, it really breaks classless IP.

But that's just IMHO. :slight_smile:

-Jon

We're also using the following extended access list (along with
anti-spoofing filters) to prevent smurf attacks from originating from our
network:

access-list XXX deny ip any 0.0.0.255 255.255.255.0

Folks, this is a bad idea. There are lots of completely valid IP
addresses out there that end in .255. True, most of them that
end in .255 ARE broadcast addresses, but if people implement this
kind of filtering on a large scale, it really breaks classless IP.

Eep, this is true. (Stupid me).

Haven't had any complaints yet from users unable to access anything yet,
but so much for making the 'Net slightly safer from this crap.

Jordyn

Well, I'm not so sure it is a bad idea in all cases. Like anything, you
should apply this with a little forthought, however. If you know how your
network is configured, if you know how people have carved up their class B's
and such, you can eliminate a lot of the problems by doing this kind
of thing, especially if your network is not too large. It won't stop
a broadcast sent to a network like 129.129.4.0/22 (i.e. 129.129.7.255),
and the same is true for smaller networks, but if you have a bunch of class
B's and you have carved them up into /24's, then you can catch a lot of
the problems by doing just that filter. As a general rule, for everyone,
probably not!

--Rick