dns_update_log shows dynamic entries deleted

Cuttler, Brian (HEALTH) brian.cuttler at health.ny.gov
Tue Jun 9 19:29:33 UTC 2015


I had wondered that myself, but I haven't found any evidence to support the theory (and I would much rather have a theory than an unknown).

The bind server seemed to check point its leases hourly (seems to slip back just a little each hour), and while I do see a bind restart in the logs, it was one I triggered at 09:40, there is nothing to indicate server (host or named) at the time of the event (08:18). Nor any indication that DHCPD restarted prior to my manually restarting it later on.

Nor have a found a switch to remove (auto-purge) 'old' dynamic entries, in the named.conf, though I could have overlooked it, certainly I did nothing to enable such a switch.

It's a mystery to me.


-----Original Message-----
From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of dave c
Sent: Tuesday, June 09, 2015 3:06 PM
To: Users of ISC DHCP
Subject: Re: dns_update_log shows dynamic entries deleted

Well, you are likely asking the wrong side of the equation.

If I had to venture a guess, your DNS server reloaded itself.

Dynamic DNS updates are written to a local cache for the zone. I don't know if that cache will always persist through having DNS restarted, but I'd suggest that as it's dynamic, it's not designed to be persistent in the DNS zone. Otherwise it would be in a DNS zone file :)

Do you have any info or stats on the DNS side of things?

If you had said that you started seeing updates not getting through to DNS, then I'd suggest that the issue might be that the DHCP system and DNS system had a change in what they used to authenticate updates. But as all dynamic DNS information departed at the same time and is being recreated as systems check into DHCP, it points to the issue being on the DNS side.


On 6/9/15 13:21, Cuttler, Brian (HEALTH) wrote:
> I disabled update_optimization and as dhcp releases are renewed (I 
> already has update_static
> enabled) we are re-creating the DNS entries.
> I still have no idea why those entries all got deleted and am rather stressed over it.
> Please help me to understand what went wrong, and how to prevent or properly fix.
> Many thanks,
> Brian
> *From:* dhcp-users-bounces at lists.isc.org 
> [mailto:dhcp-users-bounces at lists.isc.org] *On Behalf Of *Cuttler, 
> Brian (HEALTH)
> *Sent:* Tuesday, June 09, 2015 12:05 PM
> *To:* Users of ISC DHCP
> *Subject:* dns_update_log shows dynamic entries deleted
> We are running on Centos 7.1 and have dhcp 4.2.5, with bind 9.9.4.
> We are running dhcp with subnet permitted dynamic dns 
> udpates, except for the last
> 100 addresses in the pool, which we excluded to allow for static addresses that we needed.
> Things have been working wonderfully - but at 08:18 this morning a 
> large number of entries were removed from dynamic dns.
> The dhcp clients were either, only asleep for the night (Windows, 
> printers) or actually online (linux).
> I've no idea why these DNS entries were removed, exactly how to get 
> them back, and how to prevent them from being removed again.
> I'd suspect it was a lease expiration issue, but these machines all 
> check in and renew, at least they should be, I can check the boot.log and see.
> Thanks for your help,
> Brian
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users

Dave Calafrancesco
dhcp-users mailing list
dhcp-users at lists.isc.org

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