Re: Networks ignoring prepends?

[Robert Raszuk <robert () raszuk net>]

Bill,


> https://datatracker.ietf.org/doc/html/rfc4271#section-9.1.2.2
>
> "a) Remove from consideration all routes that are not tied for having
> the smallest number of AS numbers present in their AS_PATH
> attributes."
>
> So literally, the first thing BGP does when picking the best next hop
> is to discard all but the routes with the shortest AS path.


Not really. I have never seen a BGP implementation which would do that.
That section 9 you are referring to is just informational - no specific
order in there is mandated.

Shortest AS-PATH is used as step 4 or 5 in best path selection - not to
mention Cost Communities which below links do not even consider:

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/bgp/topics/concept/routing-protocols-address-representation.html

Thx,
R.