[arin-ppml] implementing RPKI prefix validation actually increases risk

Michel Py michel at arneill-py.sacramento.ca.us
Tue Jun 6 00:41:57 EDT 2023

Hi David,

> David Farmer wrote :
> Isn’t this why there is SLURM, RFC 8416, I think you should be able to cause the RTBH feeds to be locally Valid from an RPKI point of
> view and then prefer them in BGP. I think you could create with max prefix length 32 ROA for the RTBH feed ASNs.
> That or two /1 prefixes with a max prefix length 32 ROAs, should do the trick, if I’m understanding your issue correctly.

You do. That could work, if I could figure out a way to configure it. The choice of the RTR validator has not been made yet; I am currently using FORT for tests, but that may not be the final choice.
There are a limited number of ASNs that feed RTBH prefixes, so a small number of prefixAssertions could be handled.

> Hope that helps.

It does, thanks. I will revisit it (explored it earlier without success); I was hoping to resolve this on the routers, not having to tinker with the RTR validator.
In your experience, are SLURM files compatible between different RTR implementations ?


On Mon, Jun 5, 2023 at 21:29 Michel Py via ARIN-PPML <mailto:arin-ppml at arin.net> wrote:
Hi folks,
I am bumping into a dark side of RPKI prefix validation that actually increases risk to the network when deployed.
As many others here do, I use BGP blackhole feeds (RTBH). This technique has been around for a long time.
It is quite a common situation in some orgs to have the in-house SIEM/IDS redistribute blackhole prefixes via a BGP feed.
Also, there are numerous publicly available ones such as :
When configuring RPKI validation, here is what happens. is a real-world example of a prefix that has been blacklisted by three different RTBH feeds.
After implementing RPKI validation, it has generated some volume of firewall alarms for different type of attacks.
c4321-michel#sh ip bgp | beg 152.89.196.
BGP table version is 48156064, local router ID is
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found
      Network          Next Hop            Metric LocPrf Weight Path
I*                0     90      0 21719 I              <== Trusted RTBH
N* i                              100      1 i                    <== CBBC
I*                           0     40      0 65190 i              <== Spamhaus
V*>                           30      0 1299 9002 57523 i    <== Prefix from full feed
The problem here is that RPKI validation is at the very top of the BGP bestpath decision process, before weight and local-preference, without any way to change that.
Therefore, the “Valid” status of the RPKI route affectively renders the RTBH feeds useless. No matter what manipulations of other parameters may be configured in route-maps, the RPKI status will override everything else.
Unsurprisingly, Cisco says that doing something about it is impossible.
Unfortunately, the “Valid” RPKI status presents no warranties whatsoever that the prefix is not used for rogue activities. Same as HTTPS certificates, crooks and spammers have realized that a ROA was a necessary part of doing their dirty business.
This particular prefix is a well-known source of attacks; there are very valid reasons it is present in multiple BGP blackholes. Unfortunately, RPKI validation, combined with Cisco’s implementation, as provided bad actors with a tool to disable a blacklisting method that plenty of orgs are currently using.
I am forced to disable RPKI prefix validation. To me, RPKI prefix validation does not bring enough value to compensate for the loss of the protection that the BGP blackhole feeds provide. Implementing RPKI validation has actually increased the volume of attacks on my network, attacks that were previously blocked right at the very edge. The risk increase is immediate : implementing RPKI validation is what made me look at these new firewall alarms. On the other hand, the gain is not immediately perceptible.
In terms of public policy and ARIN, I think that there is a consensus that deploying RPKI validation is good for everyone. I am posting this so that the community can build an understanding of why it may not be deployed universally. I am not deploying it because I don’t want it or don’t understand it, I am not deploying it because it simply does not work for me. I don’t think I will be the only one in that case. It looked like a good idea on paper, but the impossibility to accommodate currently implemented security measures is a no-go.
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David Farmer               mailto:Email%3Afarmer at umn.edu
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