Thank you all for answering. I was disregarding Local Pref because the route server I was on was showing 100. That was an error on my part though as it clearly states in the login banner that it is eBGP peering with the AT&T routers hence the local Pref would go back to 100 from its perspective. Again, thanks for the quick and thorough responses. On Thu, Sep 24, 2015 at 10:05 AM, Blake Hudson <blake@ispn.net> wrote:
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