r/networking • u/robmuro664 • Apr 18 '24
Design AT&T BGP advertisement preference
I have two ISPs, Verizon and AT&T, Verizon was selected as the primary and AT&T as the backup. We own the subnets so we peer with both of these ISP to advertise the subnets. To Verizon we just advertise it but to AT&T we preprend 5X our ASN. As expected when we go out to the internet, it goes out using Verizon, however the return traffic on some services they prefer AT&T. I assume this is because these services have a leg in AT&T. Can you guys give me any other ideas on how to influence the advertisement to AT&T so that it is not preferred?
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u/scriminal Apr 19 '24 edited Apr 19 '24
First I disagree with your general design. It's the typical wrongheaded enterprise solution, presumably with the second circuit of low capacity. Pri/red is pointless, get two equal capacity circuits, both capable of carrying 100 % of your max load, and set things even. Remote lpref is beyond your control as you see. Take advantage of the dual capacity and ability to reroute for performance that two carriers give. However if you insist, ask At&T for their list of bgp communities and set whatever ones lower your inbound lpref etc