BGP Best Path Algorithm

1. Introduction
2. Level II
   1. Sub-Level A
      1. detail 1
      2. detail 2
   2. Sub-Level B
   3. Sub-Level C
      1. detail 1
         1. sub-detail a
            1. micro-detail i
            2. micro-detail ii
         2. subdetail b
      2. detail 2

 

Introduction

The 'best path algorithm' is used to narrow a list of routes down to 1 and only 1 best path. The list is composed of a set of criterion that are used for breaking ties between routes with equal costs.

 

The Algorithm (simplified Cisco)

1. Largest Weight
   1. Set by the administrator
   2. Proprietary to Cisco
   3. Not passed to other routers (local metric)
2. Highest LOCAL_PREF (defaults to 100)
3. Prefer routes aggregated with network or aggregate-address commands. Prefer network over aggregate-address.
4. Shortest AS_PATH.
5. Lowest ORIGIN type: IGP > EGP > INCOMPLETE

 

 

 

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