Arista EOS – BGP remove-private-as

By | August 9, 2019
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This is a post copied/stolen/updated from Kevin Wang’s wiznote – [EOS] [RFC6996] BGP remove-private-as. 

Summary:

  1. Feature support starts from 4.19.1F and 4.18.4F
  2. “remove-private-as” works for both 2B/4B AS#. 
  3. Private AS number: 64512-65534(2B), 4200000000-4294967294(4B). convert to asdot notation is 64086.59904.
  4. “neighbor x.x.x.x remove-private-as” only works for those as-path which only have private as number present.
  5. 3. In case you have both public as number and private as number, you need give the keyword “all” to force remove all private as number within the as-path-list. “neighbor x.x.x.x remove-private-as all”
  6. 4. If you want to keep the as-path length, using replace-as. “neighbor x.x.x.x remove-private-as all replace-as”
  7. 5. If the AS_PATH contains the AS number of the eBGP neighbor, BGP does not remove the private AS number.
  8. 6. If the AS_PATH contains confederations, BGP removes the private AS numbers only if they come after the confederation portion of the AS_PATH.
  9. If the eBGP neighbor using private as number which you intend to apply “remove-private-as”, you will get below warning message, but the CLI still able to apply and functionality also works as expected, the reason why we have this warning before it may create potential loop, because on local switch, you remove all private-as number which might be include peer’s ASN, in this case, the loop will happen, so that’s why we put the warning here.
  10. If you configured remote-as on peer-group, and peer inherit that information from peer-group, in this case, remove-private-as on peer will not prompt warning, because that’s inherit information, EOS will not check it.

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