Theorical question about cyclic dependency in IRR filtering

Mon Nov 29 13:14:08 UTC 2021

Hi Anurag,

Circular dependencies definitely are a thing to keep in mind when designing
IRR and RPKI pipelines!

In the case of IRR: It is quite rare to query the RIR IRR services
directly. Instead, the common practise is that utilities such as bgpq3,
peval, and bgpq4 query “IRRd” (https://IRRd.net) instances at for example
whois.radb.net and rr.ntt.net. You can verify this with tcpdump. These IRRd
instances serve as intermediate caches, and will continue to serve old
cached data in case the origin is down. This phenomenon in the global IRR
deployment avoids a lot of potential for circular dependencies.

Also, some organisations use threshold checks before deploying new
IRR-based filters to reduce risk of “misfiring”.

The RPKI case is slightly different: the timers are far more aggressive
compared to IRR, and until “Publish in Parent” (RFC 8181) becomes common
place, there are more publication points, thus more potential for operators
to paint themselves into a corner.

Certainly, in the case of RPKI, all Publication Point (PP) operators need
to take special care to not host CAs which have the PP’s INRs listed as
subordinate resources inside the PP.

See RFC 7115 Section 5 for more information: “Operators should be aware
that there is a trade-off in placement of an RPKI repository in address
space for which the repository’s content is authoritative. On one hand, an
operator will wish to maximize control over the repository. On the other
hand, if there are reachability problems to the address space, changes in
the repository to correct them may not be easily access by others”

Ryan Sleevi once told me: "yes, it strikes me that you should prevent
self-compromise from being able to perpetually own yourself, by limiting an
attacker’s ability to persist beyond remediation."

A possible duct tape approach is outlined at
https://bgpfilterguide.nlnog.net/guides/slurm_ta/
However, I can’t really recommend the SLURM file approach. Instead, RPKI
repository operators are probably best off hosting their repository
*outside* their own address space.

Just like with Authoritative DNS servers, make sure you also can serve your
records via a competitor! :-)

For example, if ARIN moved one of their three publication point clusters
into address space managed by any of the other four RIRs, some risk would
be reduced.

Kind regards,

Job

On Mon, 29 Nov 2021 at 13:37, Anurag Bhatia <me at anuragbhatia.com> wrote:

> Hello everyone,
>
> While discussing IRR on some groups recently, I was thinking if there can
> be (and if there is) cycling dependency in filtering where IRR (run by
> whoever APNIC, RIPE, RADB etc) uses some upstream and accepts only routes
> with existing & valid route object.
>
>
>
> So hypothetical case (can apply to any IRR):
>
>
>    1. APNIC registry source is whois.apnic.net and points
>    to 202.12.28.136 / 2001:dc0:1:0:4777::136. The aggregate of both these has
>    a valid route object at the APNIC registry itself.
>
>    2. Their upstreams say AS X, Y and Z have tooling in place to
>    generate and push filters by checking all popular IRRs. All is well till
>    this point.
>
>    3. Say APNIC has some server/service issue for a few mins and X Y and
>    Z are updating their filters at the same time. They cannot contact
>    whois.apnic.net and hence miss generating filters for all APNIC IRR
>    hosted prefixes.
>
>    4. X, Y and  Z drop APNIC prefixes including those of IRR & the loop
>    goes on from this point onwards.
>
>
> So my question is: Can that actually happen?
> If not, do X, Y and Z and possible all upstreams till default-free zone
> treat these prefixes in a special manner to avoid such loop in resolution?
>
>
>
>
> Thanks!
>
> --
> Anurag Bhatia
> anuragbhatia.com
>
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