Service Providers behaviour for dual homed enterprises

[jared at puck.nether.net (Jared Mauch)]

> On Sep 23, 2015, at 5:38 PM, Jason Bullen <jmbullen21 at gmail.com> 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?

Yes.