[nsd-users] nsec3 hash collision

W.C.A. Wijngaards wouter at nlnetlabs.nl
Mon Feb 6 08:40:29 UTC 2017

Hi Fredrik,

Change the nsec3 salt at the zone signer for this zone.

The sender is sending queries for a nonexist name that hashes (exactly)
to the same hash as the hash for an existing name in the zone.  This is
what NSD logs.  With this printout you can figure out that the short
NSEC3-string for the query name, and the nsec3 string for one of the
names in your zone, have the same hash.

NSD has replied SERVFAIL to that client, since an NSEC3 nonexistance
proof is impossible.  So, no issues except the log file spam.

At what verbosity level should I log these messages, you would think?
Then I'll fix the code for that.

Best regards, Wouter

On 03/02/17 21:40, Fredrik Pettai wrote:
> Hi,
> I noted that one of our name servers slaving customer zones started to spew these messages over and over again:
> ...
> [2017-02-03 18:16:03.069] nsd[27083]: error: nsec3 hash collision for name=ad.xxxxxx.se.
> [2017-02-03 18:16:03.078] nsd[27083]: error: nsec3 hash collision for name=ad.xxxxxx.se.
> [2017-02-03 18:16:03.111] nsd[27083]: error: nsec3 hash collision for name=ad.xxxxxx.se.
> And it’s filling up the log file very fast...
> It’s probably true and perhaps a real problem at the customer side, but does nsd really need to log 20+ lines with this message every second?
> I’ve upgraded to nsd 4.1.14 to check if the error (messages) would go away, but doesn’t seem to affect neither the issue, nor the amount of “spam” nsd pushes to the log file…
> So, could nsd please not dos itself with these messages? :)
> Re,
> /P
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> nsd-users at NLnetLabs.nl
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