When receiving BGP updates from two peers with different AS paths and MED values, how will the router determine which path is preferred?

In BGP (Border Gateway Protocol) route selection, several criteria are evaluated to determine the preferred path when multiple routes to the same destination are available. When comparing paths from different peers, the deciding factors include AS paths, next-hop attributes, and Multi-Exit Discriminator (MED) values.

When the router receives updates from different peers with unique AS paths and MED values, it first considers the AS path length. Generally, the path with the shorter AS path is preferred. If the AS paths are of equal length, then the router will compare the MED values. The path with the lower MED value is preferred if both paths lead to the same destination but come from different autonomous systems.

In the scenario where one path has a shorter AS path, that path will be chosen even if its MED is higher than the other path. Thus, if Peer A provides a route with a shorter AS path compared to Peer B, that route through Peer A will be favored for all traffic to that destination, overriding considerations of the MED values.

This understanding leads to the conclusion that the path through Peer A is indeed the correct choice for all traffic to that destination, reflecting the BGP decision-making process.