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BGP ECMP route sharing for different uplink to AS Not Working On EXOS or S-Series Router

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TitleBGP ECMP route sharing for different uplink to AS Not Working On EXOS or S-Series Router
Symptoms
  • Client wants to receive the same routes from 2 different ISP's and load share the traffic
  • All traffic  to destination forwarded to only one next-hop router
Environment
  • EXOS All
  • S-Series
  • BGP
Cause
The BGP Equal Cost Multi-path (ECMP) feature supports load sharing by creating a multipath to a destination. This multipath contains multiple routes that are determined to have an equal cost because the following parameters are the same for each route:
  • Weight
  • Local preference (for IGBP multi paths)
  • AS path (entire attribute, not just the length)
  • Origin code
  • Multi Exit Discriminator (MED)
  • IGP distance to the next hop
  • Source session (EGBP or IGBP)
In this case, the AS path is not the same, so the routes will not be considered equal cost.
Resolution
If both ISPs advertise the same AS number, this will work. However, this may not be a feasible solution.
Additional notes

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