[c-nsp] IOS XR BGP

[Gert Doering]

Hi,

On Tue, Nov 29, 2011 at 10:16:41PM +0800, Mark Tinka wrote:
> On Tuesday, November 29, 2011 09:40:30 PM Gert Doering 
> wrote:
> 
> > Most ISPs these days do not seem to have customers that
> > use BGP-based multihoming using networks from the ISP's
> > PA blocks - but of course, exceptions happen (we have
> > one customer that uses an IPv6 /48 from our /32 due to
> > historic reasons).
> 
> We do have some customers that announce our own space back 
> to us because they multi-home to us and need some kind of 
> independent route control.

Well, yes.  This is a scenario we have, of course, but I didn't
think of it because customer BGP sessions have completely different
- and very strict - route filters.

Customer session:
  "customer may only announce a well-defined set of prefixes"

Peering or Upstream
  "we accept most prefixes except for well-defined things we do not
   want, like 224.0.0.0/6, subnets of our own address blocks, subnets
   of IXP prefixes we're at, etc."


So, if a customer is multihomed *to us*, and uses Space from our aggregates,
this will be fine - different set of filters, and the routes are not 
supposed to propagate anyway (when these filters are built, the "export
to world" community is not set, but "no-export" instead).

If a customer is multihomed to us and to some *other* ISP, and uses space
from our aggregate, we need to open the "Peering or Upstream" prefix filter
to take that into account.  But that's not a typical case for us.

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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