BGP prefix filter list

Saku Ytti saku at
Thu May 30 17:36:46 UTC 2019

Hey William,

> Error #1: section 4.
> It's permissible to announce to your transits with a private AS which they remove before passing the announcement to the wider Internet. As a result, the announcement from each provider will have that provider's origin AS when you see it even though it's actually from a downstream multihomed customer.

This may not be common interpretation of the section you cite.
Remove-private-asn implementation (CSCO, JNPR) does not remove
privates after head. As your transit provider will receive head having
your public ASN, they cannot remove any subsequent private ASNs. Only
one who can remove private-asn is the originator. Your transit
provider can only drop the route or propagate route with private asn
in it.

It would be inadvisable to send paths with private ASN to your transit
operator, as not all transit operators are comfortable propagating


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