CloudFlare issues?

Sat Jul 6 20:05:23 UTC 2019

On Thu, Jul 04, 2019 at 11:46:05AM +0200, Mark Tinka wrote:
> I finally thought about this after I got off my beer high :-).
> 
> Some of our customers complained about losing access to Cloudflare's
> resources during the Verizon debacle. Since we are doing ROV and
> dropping Invalids, this should not have happened, given most of
> Cloudflare's IPv4 and IPv6 routes are ROA'd.

These were more-specifics, though.  So if you drop all the
more-specifics as failing ROV, then you end up following the valid
shorter prefix to the destination.  Quite possibly that points at the
upstream which sent you the more-specific which you rejected, at which
point your packets end up same going to the same place they would have
gone if you had accepted the invalid more-specific.

Two potential issues here:  First, if you don't have an upstream who
is also rejecting the invalid routes, then anywhere you send the
packets, they're going to follow the more-specific.  Second, even if
you do have an upstream that is rejecting the invalid routes, ROV won't
cause you to prefer the less-specific from an upstream that is
rejecting the invalid routes over a less-specific from an upstream that
is accepting the invalid routes.

For example:
   if upstream A sends you:
      10.0.0.0./16 valid
   and upstream B sends you
      10.0.0.0/16 valid
      10.0.0.0/17 invalid
      10.0.128.0/17 invalid
you want send to send the packet to A.  But ROV won't cause that, and if
upstream B is selected by your BGP decision criteria (path length,
etc.), you're packets will ultimately follow the more-specific.

(Of course, the problem is can occur more than one network away.  Even
if you do send to upstream A, there's no guarantee that A's
less-specifics aren't pointed at another network that does have the
more-specifics.  But at least you give them a fighting chance by
sending them to A.)

     -- Brett