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 <bl...@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 >