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

Jason Schiller schiller at uu.net
Wed Oct 31 17:43:00 EDT 2007

Ted Mittelstaedt wrote:
> It's unlikely that if the routing
> table grows past existing ISP equipment that it would result in
> ISP bankruptcies.  A far more likely scenario among the smaller
> cash-poor ISP's is it will encourage single homing with the resultant
> lowering of Internet reliability for customers of those ISPs.

When routing slots become scarse we all will have the difficult decesion
of which routes to install.  

It is my suspicion that ISPs will discard non-customer routes first before
customer routes.  The first set of routes likely to be discarded are
non-customer routes that are a more specific of an aggregate.  This will
break TE.  The next set of routes likely to be discarded are non-customer

At this point, a paying customer may complain that it cannot reach some
non-customer destination.  The ISP will explain that the destination in
question is not a customer, and does not pay to have its route in the
table.  The ISP will then offer the option for his or her customer to pay
to have the route in the table, or the destination can pay to thave their
route in the ISp's table.  Talk about net neutrality issues.

On Wed, 31 Oct 2007, Scott Leibrand wrote:
> Yeah, in practice ISP filtering is the only enforcement mechanism here.
> However, as an earlier poster pointed out, ISPs currently have nothing
> to point to if they want to tell their customers that announcing their
> covering aggregates is the right thing to do.  I think it would be
> useful for ARIN to state that such behavior is expected, either in the
> NRMP or the upcoming NPOG.

It would be nice to have a NPOG to reference to try and persuade people to
do the right thing.

On Wed, 31 Oct 2007, Scott Leibrand wrote:
> I don't think that's true.  Today, anything you advertise in IPv4 down
> to a /24 will be accepted more or less by everyone.  However, that's
> only a convenience for optimal TE.  In order to just maintain
> reachability, all you really need is for your upstreams (all your
> transit providers and all their transit providers) to accept your
> deaggregated routes from you and from each other.  The rest of the world
> need only accept the RIR-assignment-size covering aggregate, route the
> traffic toward one of your transit providers, and then let the
> more-specifics take over when they hand the traffic off to them.

For large ISPs with widespread peeing, and lots of mult-homed customer
overlap, this basiclly means they need to carry nearly all of the routes.


Jason Schiller                                               (703)886.6648
Senior Internet Network Engineer                         fax:(703)886.0512
Public IP Global Network Engineering                       schiller at uu.net
UUNET / Verizon                         jason.schiller at verizonbusiness.com

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