Nokia Network Routing Specialist II (NRS II) 4A0-114 Question # 6 Topic 1 Discussion

When a BGP router receives multiple routes for the same destination, it selects the best route based on several attributes in the following order of preference:

Highest local preference: Routes with the highest local preference are preferred.

Shortest AS_PATH: Routes with the shortest AS path are preferred.

Lowest MED: Routes with the lowest MED are preferred.

eBGP over iBGP: Routes learned via eBGP are preferred over iBGP routes.

Lowest IGP metric to BGP next hop.

Given the routes:

Local preference 100, MED 150, AS Path 65300 65200 (eBGP)

Local preference 100, MED 100, AS Path 63200 (iBGP)

Local preference 200, MED 150, AS Path 65400 63200 (iBGP)

Local preference 200, MED 100, AS Path 63700 (eBGP)

Route 4 has the highest local preference (200), the lowest MED (100), and is learned via eBGP. Therefore, it is the best route.

ReferencesNokia Border Gateway Protocol Fundamentals, Chapter on BGP Route Selection Process.