PATH SELECTION WITH BGP

A BGP speaker evaluates different paths to a destination network from its border gateways at that network, selects the best one, applies relevant policy constraints, and then advertises it to all of its BGP neighbors. A complication in Inter-AS routing does arise from the lack of a universally agreed-upon metric among ASs that can be used to evaluate external paths. Each AS may have its own set of criteria for path evaluation.

Anyway, the BGP speaker builds a routing database consisting of the set of all feasible paths and the list of networks reachable through each path. In actual BGP implementations, the criteria for assigning degree of preferences to a path is specified in configuration tasks. These tasks include configuring ...

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