CloudFlare issues?

[nanog at as397444.net (Matt Corallo)]

On my test net I take ROA_INVALIDs and convert them to unreachables with
a low preference (ie so that any upstreams taking only the shorter path
will be selected, but so that such packets will never be routed).

Obviously this isn't a well-supported operation, but I'm curious what
people think of such an approach? If you really want to treat
ROA_INVALID as "this is probably a hijack", you don't really want to be
sending the hijacker traffic.

Of course if upstreams are rejecting ROA_INVALID you can still have the
same problem one network away, but its an interesting result for
testing, especially since it rejects a bunch of crap in China where CT
has reassigned prefixes with covering ROAs to customers who re-announce
on their own ASN (which appears to be common).

Matt

On 7/6/19 4:05 PM, Brett Frankenberger wrote:
> 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
>