Clean up dynamic names

Cuttler, Brian R (HEALTH) brian.cuttler at
Wed Feb 8 20:12:58 UTC 2017

I have handled the A and PTR records before, and knew from prior DNS zone file work that the first field defaulted, just I guess some reluctance to “play” with live tables. I feel fortunate (at the times I’m not feeling frustrated) that # nsupdate does not seem to cause any side-effects and is happy to reject commands it doesn’t care for.


From: Bob Harold [mailto:rharolde at]
Sent: Wednesday, February 08, 2017 3:05 PM
To: Cuttler, Brian R (HEALTH) <brian.cuttler at>
Cc: Darcy Kevin (FCA) <kevin.darcy at>; Users of ISC DHCP <dhcp-users at>; bind-users at
Subject: Re: Clean up dynamic names

On Wed, Feb 8, 2017 at 1:09 PM, Cuttler, Brian R (HEALTH) <brian.cuttler at> wrote:

I understand. Let me refocus the question.

I know DHCP will remove the info when the old lease expires, will it remove this information for me in the case of the device falling off line, and how can I accelerate that process so that I can reassign the printer tag to a new IP address.

Knowing that I have a "A", "TXT" and "PTR" record, is # nsupdate the correct mechanism, and how do I specify the commands to remove the "TXT" record as it is missing column 1 in the tables. I have previously manually both created and removed forward and reverse records, but text records are different, I just don't know how different.

The forward table looks like this

hr16038                 A
                        TXT     "00f8e5793e94da14990f27763448c54a00"
If the first field is shown as blank, it means "same as previous", so "hr16038" in this case.
If the ttl is not shown, it is "same as last $TTL record"  (or taken from 'minimum' field in SOA if no $TTL)
If no class is shown, it is probably "IN", I forget now where it defaults that.
If the first field is not fully qualified, the domain is taken from the last $ORIGIN, or SOA?, or named.conf.
So the records if listed in full would be something like:

hr16038.somedomain.tld.    9999   IN       A
hr16038.somedomain.tld.    9999   IN    TXT     "00f8e5793e94da14990f27763448c54a00"

nsupdate is probably the best tool for removing the old records.

Bob Harold
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