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

["Alexei Roudnev" <alex () relcom EU net>]

Yes, but time when AS and AS path filters was widely used is (almost) over, so it does not produce a lot of headache 
(now the
communities and prefix lists are used more and more to control routing, not AS-es).

This routing broke some policies (because such specific prefixes can be rejected by some ISP and so the packet pathes 
are very
sofisticated sometimes), but it's not too bad. The address space is much more important resource, than bandwidth, so 
any way to
keep this space can be done in real (not theoretical) Internet.

Btw, I know a few big ISP who does not use AS-path in their filters at all. And everything work. Yiu forget to mention 
possible
routig loops (caused by such specific announces in rare cases), but I never saw it in practice.

----- Original Message -----
From: "Dmitri Krioukov" <dima () dimension net>
To: "Greene, Dylan" <DGreene () NaviSite com>; "Jesper Skriver" <jesper () skriver dk>
Cc: <nanog () merit edu>
Sent: Friday, April 07, 2000 6:04 PM
Subject: RE: Policies: Routing a subset of another ISP's address block


> 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.
> --
> dima.
>
> > -----Original Message-----
> > From: Greene, Dylan [mailto:DGreene () NaviSite com]
> > Sent: Friday, April 07, 2000 6:06 PM
> > To: 'Dmitri Krioukov'; Jesper Skriver
> > Cc: nanog () merit edu
> > 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: owner-nanog () merit edu [mailto:owner-nanog () merit edu]On Behalf Of
> > > Jesper Skriver
> > > Sent: Friday, April 07, 2000 2:21 PM
> > > To: Daniel L. Golding
> > > Cc: David Harrison; nanog () merit edu
> > > 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.