Hello list!
I'm experiencing a problem with my PowerDNS slave machines not
performing AXFRs when notified by the master of a zone reload, and I've
been unable to find any satisfactory answers. First, some of the
pertinent questions:
* What PowerDNS or dnsdist version you are using
/PowerDNS 4.0.3/
* What backends you use (gMySQL, BIND etc)
/gMySQL/
* If you are using DNSSEC
/Yes, the zones in question are signed on the master/
* Operating system it is running on
/Debian Stretch (9.1)/
* Where you got the binary from, i.e. did you compile it yourself
(which compiler, including version), from your distribution or ports
tree etc
/Using version from official Debian Stretch repositories/
The specific problem I'm having can be summed up by the following two
log lines on the slave:
> Sep 06 14:31:33 2 slave domains need checking, 0 queued for AXFR
> Sep 06 14:31:36 Received serial number updates for 0 zones, had 2
timeouts
I am triggering updates via the DHCP DDNS facility documented here:
https://doc.powerdns.com/md/authoritative/dnsupdate/#dns-update-how-to-setup-dyndnsrfc2136-with-dhcpd,
however this problem also occurs occasionally though less frequently
when I manually update a zone in the MySQL backend and trigger a
"pdnsutil increase-serial <domain>" followed by a "pdns_control reload
<domain>". This is occurring with many domains as well, though due to
the DHCP DDNS I'm focusing on only two.
I would expect zero timeouts, however at least 50% of the time both
relevant zone transfers time out as shown in the log above. 40% of the
time one times out, and only 10% of the time (based on about two dozen
tests) do both zones AXFR as expected on both slave hosts. The timeout
time is always exactly 3 seconds after the NOTIFY is received, and I've
not found any setting in the documentation to increase this time.
I did a packet capture on both sides of the transaction (both master and
slave), and I see the NOTIFY packet sent by the master and acknowledged
on the slave, however when I see the timeouts I never see the slave send
any sort of AXFR request as I would expect. The notifies are received
without error to both hosts every time. Given the lack of relevant
information in these I have not included them.
There is no firewalling or other network interruptions between the
master and slave and they are on the same broadcast domain. And as
mentioned, sometimes at least one domain succeeds and I see the AXFR
request sent from the slave to the master. This occurs intermittently
between both of my slave machines, so this does not appear to be network
related. I also confirmed that there are no errors related to the MySQL
backend on the master.
Increasing the loglevel to 9+ on both sides does not reveal any further
information as to the timeout. So ultimately, my question is: *[tl;dr]*
What exactly does "had X timeouts" mean on the slave (i.e. what is
timing out), and what can I do to diagnose the cause or prevent it from
happening?
Here is the full log from the master with loglevel=9 (with the main
domain changed here to `domain.tld` for privacy purposes; as previously
mentioned this is occurring for multiple domains anyways) for a sample
run. In this particular case, my second slave server (10.9.0.66)
properly responded with AXFR requests for both updated domains, however
the first slave server (10.9.0.65) did not. This is fairly consistent
behaviour for me regarding this problem - sometimes the first responds
with one or both, other times the second responds, but almost invariably
one zone on one host does not AXFR.
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
2 domains for which we are master need notifications
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Queued notification of domain 'i.domain.tld' to 10.9.0.65:53
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Queued notification of domain 'i.domain.tld' to 10.9.0.66:53
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Queued notification of domain '0.9.10.in-addr.arpa' to 10.9.0.65:53
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Queued notification of domain '0.9.10.in-addr.arpa' to 10.9.0.66:53
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
gmysql Connection successful. Connected to database 'dns' on
'db.domain.tld'. [3 repetitions removed]
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Remote 10.9.0.66 wants '0.9.10.in-addr.arpa|SOA', do = 1, bufsize =
1680: packetcache MISS
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Remote 10.9.0.66 wants 'i.domain.tld|SOA', do = 0, bufsize = 512:
packetcache MISS
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
AXFR of domain '0.9.10.in-addr.arpa' initiated by 10.9.0.66
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
AXFR of domain '0.9.10.in-addr.arpa' allowed: client IP 10.9.0.66 is in
allow-axfr-ips
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
AXFR of domain 'i.domain.tld' initiated by 10.9.0.66
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
AXFR of domain 'i.domain.tld' allowed: client IP 10.9.0.66 is in
allow-axfr-ips
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
gmysql Connection successful. Connected to database 'dns' on
'db.domain.tld'. [10 repetitions removed]
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
AXFR of domain 'i.domain.tld' to 10.9.0.66 finished
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
gmysql Connection successful. Connected to database 'dns' on
'db.domain.tld'.
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
Done signing: 6425.07 sigs/s,
> Sep 06 14:31:33 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:33
AXFR of domain '0.9.10.in-addr.arpa' to 10.9.0.66 finished
> Sep 06 14:31:34 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:34
Removed from notification list: 'i.domain.tld' to 10.9.0.65:53 (was
acknowledged)
> Sep 06 14:31:34 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:34
Removed from notification list: 'i.domain.tld' to 10.9.0.66:53 (was
acknowledged)
> Sep 06 14:31:34 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:34
Removed from notification list: '0.9.10.in-addr.arpa' to 10.9.0.65:53
(was acknowledged)
> Sep 06 14:31:34 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:34
Removed from notification list: '0.9.10.in-addr.arpa' to 10.9.0.66:53
(was acknowledged)
> Sep 06 14:31:36 dns.i.domain.tld pdns_server[30635]: Sep 06 14:31:36
No master domains need notifications
I appreciate any information or advice anyone can provide, and I am able
to reproduce this consistently should more testing be required!
Thanks,
Joshua Boniface
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