BGP Decision Process

For every prefix a BGP router receives, the first thing checked is the NEXT_HOP attribute. If the next hop is not accessible (not in the IP routing table), the prefix is rejected. For routes received from an IBGP peer, the next check after the next hop check is to see if the routes are synchronized. Unsynchronized routes are rejected only if synchronization is enabled. The following steps in the BGP decision process apply only if there is more than one route to a particular prefix:

1. Prefer the path with the highest weight

2. Prefer the path with the highest local preference

3. Prefer locally originated routes (Next Hop = 0.0.0.0)

4. Prefer the path with the shortest AS path

5. Prefer the path with the lowest origin type: IGP is lower than EGP, and EGP is lower than INCOMPLETE

6. Prefer the path with the lowest metric or MED

7. Prefer EBGP routes over IBGP routes

8. Prefer the lowest IGP metric to the next hop

9. Prefer the path from the router with the lowest router ID