validating reachability via an ISP

Wed Mar 28 23:22:55 UTC 2018

Hi all,
  I have an enterprise network and do not provide transit. In one of our
datacenters we have our own prefixes and rely on two ISPs as BGP neighbors
to provide global reachability for our prefixes.  One is a large regional
provider and the other is a large global provider.

Recently we took our link to the global provider offline to perform
maintenance on our router.  Nearly immediately we were hit with alerts that
our prefix was unreachable and BGPMon alerted that nearly 80 AS's noted our
route had been withdrawn.  We were not unreachable from every AS, but we
certainly were from some of the largest.

The root cause is that the our prefix is not being adequately
re-distributed globally by the regional ISP.  This is unexpected and we are
working through this with them now.

My question is, how can I monitor global reachability for a prefix via this
or any specific provider I use over time?  Are there various route-servers
I can programmatically query for my prefix and get results that include AS
paths? Then I could verify that an "acceptable" number of paths exist that
include the AS of the all the ISPs I rely upon.  And what would an
"acceptable" number of alternate paths be?

thanks in advance,
  -andy