validating reachability via an ISP

Thu Mar 29 14:51:37 UTC 2018

On Wed, Mar 28, 2018 at 7:22 PM, Andy Litzinger
<andy.litzinger.lists at gmail.com> wrote:
> 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 route had been withdrawn.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?

I did something similar a few years ago, by querying routeviews and
validating AS paths using python and pexpect. You could adapt it for
your use pretty easily. The code's here:

https://github.com/awentzell/check-as-path