[ppml] Effects of explosive routing table growth on ISP behavior

Scott Leibrand sleibrand at internap.com
Wed Oct 31 18:25:05 EDT 2007

Ted Mittelstaedt wrote:
> My guess is if this kind of thing ever came to pass you would see some
> kind of "dynamic filtering" come into place.  In other words, the ISP's
> BGP peer router would look at ALL inbound and outbound traffic that
> passes through it, and automatically modify the filter to allow the
> route into the table for any source or destination of any packet going
> through the router.  You would set the expiration of the "hole" in the
> filter to be proportional to the number and size of the packets and
> how long they were coming through the hole.
> Oh dear, I've probably done gone and screwed up someone's patent
> application.

Agreed.  I've asked my router vendors for such features from time to 
time.  Yet more prior art.  :-)

> But I still think that a lot of this is chicken little stuff.  Think
> of how many credit card numbers there are in the world, and how any
> of them could suddenly appear at some card swipe machine anywhere in
> the world, yet the global banking community seems to be able to
> handle this just fine.  The hardware exists to do that, it can be built
> to do this.

Agreed.  However, doesn't dynamic filtering rely on having a 
less-specific covering route, so you can at least route whatever packets 
come in until you get enough of them to start accepting more-specifics?  
I'm not worried that the routing table will explode unexpectedly, but I 
am worried about implementing policies (such as allowing transfers of 
/24s at the RIR level) that are incompatible with the kind of filtering 
that would be needed to deal with a rapid routing table expansion.


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