[Arista EOS] [RFC6996] BGP remove-private-as
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Tech Keypoint Summary
1. remove-private-as works for both 2 bytes ASN and 4 bytes ASN.
2. “neighbor x.x.x.x remove-private-as” only works for those as-path which only have private as number present.
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”
4. If you want to keep the as-path length, using replace-as. “neighbor x.x.x.x remove-private-as all replace-as”
5. If the AS_PATH contains the AS number of the eBGP neighbor, BGP does not remove the private AS number.
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.
7. Private AS number: 64512–65534(2B), 4200000000–4294967294(4B). convert to asdot notation is 64086.59904.
8. 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.
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.
nv415.09:56:59(config-router-bgp)#neighbor ixia_65513_v4 remove-private-as! eBGP neighbor has a private AS numbernv415.09:57:11(config-router-bgp)#neighbor 201.13.1.2 remove-private-as
RFC6996 defined private 4 Bytes ASN
https://tools.ietf.org/html/rfc6996
5. IANA Considerations
IANA has reserved, for Private Use, a contiguous block of 1023
Autonomous System numbers from the "16-bit Autonomous System Numbers"
registry, namely 64512 - 65534 inclusive. IANA has also reserved, for Private Use, a contiguous block of
94,967,295 Autonomous System numbers from the "32-bit Autonomous
System Numbers" registry, namely 4200000000 - 4294967294 inclusive. These reservations have been documented in the IANA "Autonomous
System (AS) Numbers" registry [IANA.AS].
