dhcp/dynamic-dns "hostname/domain" issue

Cuttler, Brian (HEALTH) brian.cuttler at health.ny.gov
Tue Feb 10 21:01:40 UTC 2015

I believe I have resolved my problem. I am now registering forward and reverse records for domain compliant machines with my domain name.

This man page finally tripped the right circuit in my head.


The issue was that we were, by default, allowing client updates, setting the ignore flag seems to have fixed the issue.

I have not resolved by debug “log” statement issues, suspect that I need to use
   log(info, concat(ddns-domainname));

and will test, but that is no longer critical

Thank you,

From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Cuttler, Brian (HEALTH)
Sent: Tuesday, February 10, 2015 3:12 PM
To: Users of ISC DHCP
Subject: FW: dhcp/dynamic-dns "hostname/domain" issue

I sent this earlier, and thought it hit my inbox, but I don’t see it…

I’ve updated the subnet statement for debugging purposes. Please see below.

I’m running isc dhcp 4.2.5 on Centos 7, and named 9.9.4.

Our computers all know their names, which are their inventory barcodes ex, “cs00123”, “hr45678”

While simple machines like printers or basic computers have no problems registering with DHCP, and having their information entered in named, we are seeing that the computers that are connected to the local domain server are providing client names of “cs00123.Health1.HCOM.Health.State.NY.US.”.

This does not seem to be an issue for DHCP, but we are registering DNS Reverse records of cs00123.health1.hcom.health.state.ny.us and not registering forward records at all.

I’d thought that I could re-write the address by specifying the following in the subnet

ddns-hostname = substring (option host-name, 0, 7);
ddns-domainname = “esp22.wadsworth.org”;

again, this works fine for printers, and non-domain computers.

We would like the domain member computers to have forward and reverse records of in a   cs00123.wadsworth.org. in ptr cs00123.wadsworth.org.

And not healt1.hcom….us

I will include the full zone and subnet info.

Any help to debug/fix this issue would be appreciated.

n  I have added the “log()” messages and restarted the server, I see that the edited hostname comes back as expected, but the other log messages do not cause anything to be put to my log file.

I suspect this is a matter of default and/or priority of how things are declared, but I can’t seem to find the info I need to get things working as we’d like.

zone esp22.wadsworth.org. {
key dhcpupdate;

#### default_vlan at ESP, Vlan 22
subnet netmask {
#use-host-decl-names on;
option routers;
        ddns-hostname = substring (option host-name, 0, 7);
        ddns-domainname = "esp22.wadsworth.org";
        ddns-rev-domainname "in-addr.arpa.";
        option domain-name-servers, admin.wadsworth.org, bionsc.wadsworth.org, ldap1.wadsworth.org;
log(info,concat("hostname ", ddns-hostname));
log(info,concat("domain name ",ddns-domainname));
log(info,concat("edited name ",substring(option host-name,0,7)));
        pool {
                allow unknown-clients;
                allow known-clients;
#                deny dynamic bootp clients;
        option domain-name-servers,, admin.wadsworth.org, bionsc.wadsworth.org, ldap1.wadsworth.org;

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