Service Providers behaviour for dual homed enterprises

Thu Sep 24 14:49:00 UTC 2015

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
>