validating reachability via an ISP

Thu Mar 29 05:00:22 UTC 2018

On 3/29/2018 2:22 AM, Andy Litzinger 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 route had been withdrawn.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?

If your global provider supports, you could send your announcements with
a BGP community per RFC1998 telling them to not-prefer-so-much that
advertisement, "use it as a backup".

that would shift a lot of incoming traffic to the other link (regional
provider).
You'll still have the global provider link.
this is a smaller change towards taking global provider offline, keeping
some fallback.

Frank