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BGP Path Selection Algorithm

In this discussion we will dive into the BGP Path Selection Algorithm. There are 3 (Rejection, Selection, Tie-Break) rounds of BGP Path Selection which involve 18 different steps. The first round is Rejection where any route matching certain condition will be rejected. The second Round is Selection where BGP Best Path Compiler will choose a path matching certain conditions. The last round is Tie-Break where the BGP Best Path Compiler will make the final decision based on certain criteria. Rejection Round Any roues matching the following conditions will be rejected by default. The above behavior can be changed with explicit configuration. We will discuss each with an example in another tutorial. Selection Round In this steps one route will be preferred over another in case it fulfill the any of the below conditions which include certain Path Attributes and other constraints. You can further remember the steps with the following […]

 bgp-pa bgp-path-attribute bgp-path-selection path-attribute 

Selection of iBGP & EBGP Paths

In a situation where a route coming from both ebgp and ibgp peer, the best path election will takes place in two different way. If the rote is locally originated then it will prefer ibgp path, otherwise it will chose ebgp path.

 BGP Distance bgp-path-selection iBGP over EBGP prefer iBGP over EBGP