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RE: Policies: Routing a subset of another ISP's address block

  • From: Dmitri Krioukov
  • Date: Fri Apr 07 20:52:39 2000

it does generate inconsistent origin as'es and it does break
path filters, but not only. it breaks all the tools/methods
based on the uniqueness of the route->origin-as mapping. i'm
looking for a more or less complete list of these tools/methods.

it seems, though, that the inconsistent-as list is growing and
this doesn't produce too much panic.

and if you examine this list more closely, you'll notice that it
looks like the major part of it is generated by the isps doing
the aforementioned trick.

> -----Original Message-----
> From: Greene, Dylan [mailto:[email protected]]
> Sent: Friday, April 07, 2000 6:06 PM
> To: 'Dmitri Krioukov'; Jesper Skriver
> Cc: [email protected]
> Subject: RE: Policies: Routing a subset of another ISP's address block
> Hey there..
> I'd imagine this works fine, but doesn't it leave you w/ inconsistent-as,
> where you've got a prefix being advertised from the private ASN,
> stripped &
> replaced w/ each upstream ASN?
> I mean, it should work, but is it a very good idea? The
> inconsistent-as list
> isn't _too_ big right now, which is good, as each one effectively breaks a
> number of common path filters. But if that starts to becomes common
> practice, the list gets bigger and bigger & more filters get broken.
> ..Dylan
> > -----Original Message-----
> > From: [email protected] [mailto:[email protected]]On Behalf Of
> > Jesper Skriver
> > Sent: Friday, April 07, 2000 2:21 PM
> > To: Daniel L. Golding
> > Cc: David Harrison; [email protected]
> > Subject: Re: Policies: Routing a subset of another ISP's address block
> >
> > Actually I've helped quite a few such customers, my recommendation
> > usually is to get PI space from RIPE, and get both providers to announce
> > it from their ASN, this works quite well, and also save a ASN - if the
> > customer really want to run BGP, we have arrangements with other ISP's
> > here, that we find a private ASN (that none of us use currently), and
> > assign this ASN to the customer, and we then strip the private ASN on
> > the edges of our network.
> this is interesting (since it overwrites the rule that multihoming to two
> isps requires a public asn assignment) and i've tested exactly
> this scenario
> (again, a customer uses some private asn and is peering with two isps;
> both of them strip this asn at their boundaries (remove-private-as))
> in my lab before and it worked fine. it results in propagating routes to
> the same networks with two distinct as path attributes, though. i've been
> looking for any operational experience with this setup. so, do you claim
> that you couldn't detect *any* problems with this setup?
> --
> dima.