On Fri, Apr 13, 2018 at 10:35 PM, Randy Bush <randy@psg.com> wrote:
I believe we've seen bogus low AS number announcements a few times before, and they've usually been caused by attemts to configure AS path prepending without understanding and/or reading the docs.
Someone might have wrongly assumed that
set as-path prepend 133711 133711
could be written shorter like
set as-path prepend 133711 2
and there you go...
for someone else's prefix?
Perhaps their policy is something like: "prepend all of transit-provider-1 prefixes by 2, their links are crappy today" followed by output policy: "permit all of my prefixes (matched by as-path-regex) and my customer prefixes (matched by community)" there's probably a bunch of ways this can go sideways, that's just one simple (and seen before) example.