Below is the BGP best path selection criteria :
1. If we are having only single route for destination then this route will be select without any condition.
2. Weight :- If we are having more than one routes for the same destination. Then a route with the highest weight value will be select.
3. Local Preference :- If weight values is same of all the routes then a route with highest local preference will be select.
4. Locally Originated Route :– If local preference value is also same then a locally originated route will be select.
5. AS-Path :– If there is no locally originated route then a route with smallest as-path length will be select.
6. Origin :– If all the routes are having as-path length then a route with higher preference origin code will be select.
7. MED :– If origin code is also same then a route with lowest MED values will be select.
8. Next-hop :– If MED values is same then a route with lowest IGP cost for next hop will be select.
9. Old Route :– If IGP metric is also same then a oldest route will be select.
10. Lowest Router ID :– If all the routes were received at the same time then a route with lowest router ID will be select. If we are using route reflector. Then a route with highest originator ID will be select.
Please remember that router will follow the basic route selection criteria. So first , it will check the prefix for longest match then it will check for lowest administrative distance and finally it will check the BGP route selection criteria.
Below is path path selection flow:
I hope , now you are much families with bgp best path selection process.
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