[dns-operations] anybody awake over at comcast.net?

Matt Nordhoff mnordhoff at gmail.com
Wed Feb 10 03:37:47 UTC 2021

On Wed, Feb 10, 2021 at 1:44 AM Peterson (AWS), Alec via
dns-operations <dns-operations at dns-oarc.net> wrote:
> +1 for short RRSIG times and the discipline it enforces.  We went down this path when building DNSSEC for Route 53, ZSK signatures are on the order of 10 hours:
> hilander.com. 3599 IN RRSIG DNSKEY 13 2 3600 20210210090000 (
> 20210209230000 38680 hilander.com.
> 3H3QZt3qC2XbqkbumqsvRVeVrtgJVVRVGC/TZkc7vMuN
> IdlL/wZrw+qBfYaSOex7dOp2PUP7pwW+NUgCXc2F7Q== )
> A bunch of risks with this approach that needs to be mitigated, especially around static stability in the face of an issue with the ZSK signing process.  But all solvable.  As part of this we also automated ZSK rotation (which happens less often, but still on the order of once a week).

Speaking of which, the DNSKEY RRSIG lifetime should be 11 hours, not
10 hours. The current expiration doesn't allow for client caching plus
clock skew. E.g.:

23:59:59: Recursive resolver queries authoritative servers for
hilander.com DNSKEY, gets back record set with TTL 3600, RRSIG
inception 15:00:00, expiration 01:00:00.
(00:00:00: Authoritative servers switch to new DNSKEY record set, TTL
3600, inception 23:00:00, expiration 09:00:00.)
00:59:58: Validating stub resolver queries recursive resolver for
hilander.com DNSKEY. gets back cached record set with TTL 1, RRSIG
inception 15:00:00, RRSIG expiration 01:00:00.

If the stub resolver's clock is 3 seconds fast -- 01:00:01 -- and it
doesn't make an extra allowance for expired records or clock skew, it
will treat the record set as bogus.

(All other records except for DNSKEY are live signed, with the RRSIG
expiration set 1 hour after the TTL.)


> On Feb 8, 2021, at 9:27 PM, Paul Vixie <paul at redbarn.org> wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> On Mon, Feb 08, 2021 at 01:45:06AM -0500, Viktor Dukhovni wrote:
> ...
> I do not recommend either X.509 certificate or RRSIG lifetimes quite
> this long.  Shorter lifetimes IMHO promote better discipline.
> for my own zones i think i'm using one year signatures and regenerating them
> from "cron" once per week -- just to be safe. so, not better discipline unless
> you deliberately _live_ on the edge, which i think is an unwise practice.
> i expect i'll crib together some bourne shellack to check my whole signature
> chains and warn me when there's less than 72 hours remaining in any validity
> period. going into SERVFAIL like this is an operational risk i shouldn't take.
Matt Nordhoff

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