Automatic filtering - CISCO, you should think about this...

Phil Howard phil at
Sun Dec 28 18:58:12 UTC 1997

Karl Denninger writes...

> How about an interface keyword such as "auto-inbound-filter", which does
> this:
> 	At STARTUP and when the LOCAL route table changes (ie: "ip route
> 	xxx..." statements) the system looks at the interfaces, and the 
> 	local static routes, and builds an accept list for that interface.
> 	The list is stored in a "reserved" set of system access lists.
> 	Add a parmaeter which can be turned on (ie: log) which would add
> 	"log" to the end of the filter lists, so that anyone TRYING to smurf
> 	will get logged
> This would totally automate the process of inbound filtering to prevent or
> severely limit smurf attacks.
> Since filters which are based only on the source address are relatively
> cheap for the router to process, this would likely not seriously burden 
> anyone in their direct connections.
> I'd love to see something like this, and it would reduce the complaint that
> its "too hard to manage" such things.

How about having "no-auto-inbound-filter" instead, making the default in all
new versions of IOS be to run this essential level of protection, providing
a means to turn it off only for those who know they need to turn it off.

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