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Re: Filtering levels (was RE: multi-homing without the BGP (wasRE: Packet Loss))

  • From: Daniel L. Golding
  • Date: Sun Dec 17 10:19:48 2000


By doing a summary-only aggregate, you can lose routing information that
your downstreams want seen by the global internet. A good example of this
is prepending. If I only advertise a /14, then supress a /24 that is
subordinate to that block, I may fail to advertise a prepend upon that
/24 block. Paying customer don't like stuff like that.

BTW, ARIN is pretty clear that it's allocation policies are NOT intended
for use as filtering criteria. Most folks seem to get along fine,
filtering at the /24 level. It's not like most core routers at large ISPs
are 7500s with 64mb anymore. 

- Daniel Golding

On Sun, 17 Dec 2000, Travis Pugh wrote:

> On Sun, 17 Dec 2000 [email protected] wrote:
> > 
> > Depends on what class it's in.  Let me explain further.  Verio, in their
> > infinite wisdom, has decided that they are going to throw CIDR right out
> > the window.  We own  We advertise MANY smaller
> > blocks of this space obviously, and what we have found is that in that
> > space (since it is "Class A" space, remember we don't know what CIDR is
> > since we're Verio) is that Verio does not accept anything smaller than a
> > /20.  Now many of our customers run BGP with us and advertise a /24 only,
> > I guess they're SOL as far as Verio is concerned (actually if it's
> > our space they're probably going to see the larger aggregate as
> > well, so it's not as big of a deal, but still mighty annoying).  Oh, and
> > did I mention that Verio isn't even one of our peers?  Oh well.
> > 
> Maybe if you aggregated your announcements instead of feeding a /14 to us
> as /22, /23, and /24 blocks, it wouldn't be necessary to do
> minimum-allocation filtering.
> -travis