validating reachability via an ISP

Andy Litzinger andy.litzinger.lists at gmail.com
Wed Apr 4 23:24:19 UTC 2018


Hi Andrew,
  thanks for sharing your repo, it looks very relevant and I should be able
to get it to do what I want with a slight tweak to the regex's.

Hopefully the route-views collectors or some other ones I dig up will be
able to adequately show at least 3 AS path hops through my regional
provider to get to my AS/prefix.  I really want to see AS paths where there
are at least 2 different AS hops before my regional providers AS.  This
will help me feel good that the global partners of my regional ISP are
re-advertising my prefix to their peers.  Otherwise if the AS path only
includes the first and second hop upstream I can only infer that the 2nd
hop AS is accepting routes from the 1st hop AS (my regional ISP), but not
that the 2nd hop AS is actually re-advertising the route to anyone else.

thanks!
 -andy

On Thu, Mar 29, 2018 at 7:51 AM, Andrew Wentzell <awentzell at gmail.com>
wrote:

> 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 route had been withdrawn.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
>


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