Customer sending blackhole route with another provider's AS

[chriztoffer at netravnen.de (Chriztoffer Hansen)]

Chris Adams wrote on 11/02/2020 17:30:
> Just curious what others do... I always assumed AS path filtering to
> customer (and their downstream customers) AS was a standard best
> practice.

It is.

Then again, there exists every exception to the rule you can think of.
If the exception has not been seen yet, we have not looked hard enough.

=> I.e. it depends. Is my answer. BCP is to not accept direct customer
routes 'another provider's AS in the path'. If you can reach an
agreement with the customer. You can agree to a >standardized< exception
for this single customer. <= Your dice to roll. You are the customers
upstream in this case.

AS-path rewriting on the customers side of the eBGP connection is an
option. If they remove $otherProviders ASN from the path before
(re-)announcing the black-hole routes to you. So $customerASN is seen as
the source when you receive the announcements.

Chriztoffer