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BGP Best Path Selection Algorithm


  • Check if the next-hop is reachable. If yes, then proceed
  • The path which has the highest WEIGHT
  • The path which has the highest LOCAL_PREF
  • The path which has been locally originated via a “network” or “aggregate” BGP command or through redistribution from an IGP
  • The path which has the shortest AS_PATH
  • The path which has the lowest origin type
  • The path which has the lowest MED
  • EBGP is preferred over IBGP
  • Prefer the path which has lowest IGP metric to the BGP next hop
  • Determine if multiple paths require installation in the routing table for “BGP multipath”
    In case both the paths are external, prefer the path which was received first (the oldest one)
  • Prefer the route which comes from the BGP router with the lowest router ID
    If the originator or router ID is the same for multiple paths, prefer the path which has minimum cluster list length. (This is only present in BGP RR environments. It allows clients to peer with RRs or clients in other clusters. In this scenario, the client must be aware of the RR-specific BGP attribute.)
  • Prefer the path which comes from the lowest neighbor address.

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