Re: Service Providers behaviour for dual homed enterprises

["Bob Evans" <bob () FiberInternetCenter com>]

What Blake just said below works best - I do this MED together with
small-ers all the way to india for video conferencing customers sitting in
silicon valley.

Thank You
Bob Evans
CTO




> Stephen Satchell wrote on 9/24/2015 8:39 AM:
> > On 09/23/2015 02:38 PM, Jason Bullen wrote:
> > > I've always worked in enterprise only so I thought you guys might be
> > > able
> > > to help me with this one.
> > > We are dual homed to Verizon and AT&T.  We prepend all our prefixes out
> > > AT&T to make them least preferred.  During a recent issue we found some
> > > users were coming in via AT&T.  Using various looking glasses it
> > > looks like
> > > if I use an AT&T server(route-server.ip.att.net) the best path is the
> > > prepended route through AT&T; in fact,I don't even see the VZB
> > > route.  If I
> > > use a 3rd party looking glass(router-server.he.net) I see what I
> > > anticipated, which is the shorter AS-Path through VZB.
> > >
> > > So if my research is correct, the internet prefers Verizon UNLESS
> > > they are
> > > a direct AT&T customer then they would use the AT&T circuit.
> > > Is this a standard practice that I should assume to encounter?
> > >
> > > Thanks in advance
> >
> > That's been my experience, and with other sets of providers, too.
> >
> > My current company is dual-homed with AT&T and Charter Fiber. Those
> > customers on UVerse come in the AT&T link no matter what we do with
> > BGP to convince the cloud to let packets come in the fatter pipe.
>
> Jason, while others have offered acknowledgement of the behavior you are
> seeing as well as solutions, I think it might be relevant to point out
> that this is simply a matter of BGP best path selection. BGP does not
> use AS path length (hops) as its primary path selector. Search for "bgp
> best path selection" to find out more about how BGP selects the best
> path. As others have noted, local pref is often utilized to control
> routing and should be your preferred way to control path selection in
> addition to AS path length. However, the ultimate way to control routing
> would be to advertise more specific prefixes via the path that you want
> traffic to flow.
>
> --Blake