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

Karl Denninger karl at
Sun Dec 28 18:44:23 UTC 1997

Hi CISCO :-)

I know this isn't their list, but since most major network providers run
their stuff, this is as good a place as any to talk about this.

How about an interface keyword such as "auto-inbound-filter", which does

	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.

Karl Denninger (karl at MCS.Net)| MCSNet - Serving Chicagoland and Wisconsin          | T1's from $600 monthly to FULL DS-3 Service
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