Customer sending blackhole route with another provider's AS

One of our multihomed customers is set up with some type of security
system from another upstream that can announce blackhole routes for
targeted IPs. They have a BGP policy to take those blackhole routes and
add our blackhole community string so that we can drop the traffic (and
we in turn translate to our transit providers). All good.

However, it doesn't work, because the route the customer sends to us has
the other upstream's AS as the source, and we have AS path filtering on
our customer links.

Is this a typical setup? Should we just accept the route(s) with
another provider's AS in the path? That seems... unusual. Our internal
blackhole system uses a private AS (so it can be stripped off before
sending to anyone else).

Just curious what others do... I always assumed AS path filtering to
customer (and their downstream customers) AS was a standard best

Anyone that is using blackhole communities should have enough Clue-fu
to adjust announcements along each pathway to have the correct sequence
of ASNs. Passing a route with a different upstream’s ASN as the origin, instead
of their own, is just asking for “blackhole leakage”, where they inadvertently
become a conduit for blackhole prefixes from provider A getting redistributed to
you as provider B.

Push back on them, and indicate they must pass properly-crafted AS-PATH
attributes to you in order to be accepted. If they don’t know how to do that,
a) they shouldn’t be mucking with blackhole communities, and b) they should
consider hiring Clue-fu to bring their network policies up to snuff. ^_^;


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.