BGP FLEX

Abstract

The Border Gateway Protocol (BGP) is a very important protocol in the Internet to exchange routing information between network domains.
BGP populates the routing table with valid routes, sometimes the routes populated by BGP are not the best choices specially when a ISP provides IP Transit service to an other ISP, and the two ISP are peering at an Internet Exchange Point.
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Let us assume that ISP A provides IP Transit to ISP B, and the two are peering at an Internet Exchange Point.
The return traffic from Internet to ISP B via ISP A will be routed over the Internet Exchange Point instead of the IP Transit link between the two ISP, because of BGP Local preference which has usually a higher value on Internet Exchange links.
This will lead to an issue because the return traffic IP Transit service is now passing over the Internet Exchange link.
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An other issue faced in Internet Exchange Point, is the sub-optimal routing caused by the advertisment of the most specific routes over Internet by ISP.
Let us assume that ISP A wants to advertise most specific routes to Internet for traffic Engineering, the peers of ISP A at the Internet Exchange Point could also receive the most specific routes over Internet .
This will mean that traffic from the peers of ISP A towards ISP A will now go through Internet because of most specific routes which is not suppposed to be the case.
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To solve that ISP A will have to send the same specific routes over the Internet Exchange Point which will increase complexity.
This document provides aletrnative solutions that can be used to solve the above problems¶