On Tue, Oct 10, 2023 at 12:58 PM Delong.com via NANOG <nanog@nanog.org> wrote:
Isn’t this supposed to be one of the few ACTUAL benefits of RPKI — You can specify the maximum prefix length allowed to be advertised within a shorter prefix and those (theoretically) block hijackers taking advantage of advertising more specifics to cut you off?

While I recognize that RPKI is not ubiquitous, enough of the major backbones are dropping RPKI invalids that I think any sort of hijacking in violation of that wouldn’t be very effective today.

YMMV of course, but that seems to me to be a far better solution (almost enough to make me rethink the questionable value of RPKI) than disaggregation.

Owen

Owen,

RPKI only addresses accidental hijackings.
It does not help prevent intentional hijackings. 

RPKI only asserts that a specific ASN must originate a prefix.  It does nothing to validate the authenticity of the origination.

If I am AS XX, and want to hijack a prefix from AS YY that has RPKI ROAs protecting it, and AS YY has allowed more specifics to be announced within the prefix range covered by the ROA, I'm in like flynn, because I just need to configure my router with AS YY as the origin AS, then insert the expected ASN for the neighbor adjacency with my upstreams, and bob's your uncle, the more specific prefix passes RPKI validation, and traffic comes flying my way.

If AS YY doesn't allow longer prefixes within the scope of their ROA, then it's a bit dicier, because it comes down to AS-PATH length, but there's still a good chance you can suck in traffic from your adjacent neighbors.

So yes, hijackings in violation of RPKI aren't as effective, but RPKI doesn't prevent intentional hijackings--it just protects against accidental misconfigurations and unintentional hijackings.

Thus, deaggregation is still very much part of the defensive toolbox, even with RPKI in place.

As a side note, it's also a really good reason why you shouldn't allow longer prefixes to be announced under your ROAs, except under very well understood conditions.   ^_^;

Thanks!

Matt