Purging old host names from reverse-zone file

mfoley · 12-02-2019, 01:07 PM

I'm running Slackware64 14.2, kernel 4.4.182, BIND 9.11.9.

While monitoring iftop, I noticed some old host names popping up. These are for computers that have been since has their hostnames changed, yet the new host names don't show.

I found the old host names in my reverse zone file:

Code:

52                      PTR     BRIANVM.hprs.local.
53                      PTR     DESKTOP-UMPPGUP.hprs.local.
56                      PTR     DESKTOP-NSGIEI3.hprs.local.

These IPs now have new hostnames:

Code:

192.168.0.52  MIKE.hprs.local
192.168.0.53  SUSAN.hprs.local
192.168.0.56  HOLLY.hprs.local

These host names ARE NOT in the reverse zone file, but they are in the /etc/dhcpd.conf file. E.g.:

Code:

host HOLLY {
    hardware ethernet 12:72:42:72:A2:E2;
    fixed-address 192.168.0.56;
}

and I get the right IP when looking up:

Code:

> host HOLLY
holly.hprs.local has address 192.168.0.56

# but not when reverse lookup:

> host 192.168.0.56
56.0.168.192.in-addr.arpa domain name pointer DESKTOP-NSGIEI3.hprs.local.

The old hostnames that begin with "DESKTOP-" are probably what happened when I upgraded these computers to Windows 10 (scratch install, not actual "upgrade"). They got the randomly assigned hostname Windows gives when it first boots. I then changed the computers to the correct hostname (e.g. HOLLY) when finishing the config. Interestingly, the "correct" hostname is the same name the computer had when running Windows 7, yet that old name is no longer in the reverse zone file.

So, why is the reverse-zone file not getting updated with the new/correct host names?

What can I do to fix this?

scasey · 12-03-2019, 09:47 PM

Why do you expect the maintenance of your name server to be automatic?

If there are incorrect entries in your zone files, fix them.

mfoley · 01-27-2020, 12:35 PM

Quote:

Originally Posted by scasey

Why do you expect the maintenance of your name server to be automatic?

If there are incorrect entries in your zone files, fix them.

Well, yes actually, I did expect it to be automatic. The hosts name/IP entries get into DNS x.local.zone file automatically, and the rDNS entries also apparently get in there automatically as with my example with DESKTOP-NSGIEI3.hprs.local. I didn't manually add that to the rDNS file -- it was automatic. So, yes, I did expect changes to hostnames and IPs get automatically updated.

However, if it's not automatic, it's not; regardless of my expectations. So, given that, how do you advise that I "fix them"? Is there a rndc function for this? Do I manually edit the zone file? If the latter, do I need to stop named first? I've not done this before and I've found nothing in the web to guide me.

mfoley · 01-30-2020, 01:41 AM

OK, I figured out a way to do what I want, but I'm not sure it's the "best practice" way. Using nsupdate:

Code:

> nsupdate                 
> update delete 52.0.168.192.in-addr.arpa PTR
> update delete 63.0.168.192.in-addr.arpa PTR
> update delete 102.0.168.192.in-addr.arpa PTR
> update delete 175.0.168.192.in-addr.arpa. PTR
> send

After doing this I either have to restart bind or run 'rndc -V sync -clean'. Otherwise, the changes do not "take". Does this seem right?

Also, deleting the PTR records has no effect on the A or TXT records. So, to delete an obsolete host entirely I have to (assuming that host mpress is at 192.168.0.63):

Code:

> nsupdate                 
> update delete 63.0.168.192.in-addr.arpa. PTR
> update delete mpress.hprs.local. A
> update delete mpress.hprs.local. TXT
> send

Now, in this example, host 192.168.0.63 still exists, but has a different host name: "mike". The A and TXT records are in the zone file (added automatically, I might add), but now there is no PTR record for this IP in the rDNS zone file.

Do I have to add that manually or will it eventually appear? Note that when I add a new host to the network, it does appear in the both the zone file and reverse-zone file with A, TXT and PTR records. I've never added those manually after adding a host to the network. However, not sure what the behavior will be once I deleted the PTR record for that IP.

Thots?

mfoley · 01-31-2020, 10:07 AM

More than a day later host 'mike' has not appeared in the reverse-zone-file (PTR). I added a new host 'dbserverx' to the LAN a couple of weeks ago and it automatically appeared in the zone-file (A, TXT) and reverse-zone-file. Why would 'dbserverx' get automatically added to these zone-files, but 'mike' does not?

Could really used some help from any dns/network LQ experts.