DDNS client: Multiple zone entries

[Mark Andrews]

> Hi All,
> 
> While testing the DDNS server configuration with proprietory client, I
> noticed a strange thing. I need your help to understand this.
> 
> 
> Pre-condition:
> -----------------------
> DHCP and DDNS server are running on a single Red Hat LINUX machine.
> The DHCP server was able to generate the dynamic IP Address as
> specified in the dhcpd.conf.
> DDNS server was able to add the entries in the forward and reverse zone
> files eg : testdns.com and 1.168.192.in-addr.arpa
> 
> 
> Test Condition:
> --------------------------
> I modified the host name and restarted the named service so that
> changes are reflected in the zone files. The forward zone file was
> expected to be updated with the modified host name.
> 
> Results:
> ------------
> 
> Forward zone had two entries viz; one with old host name and other with
> new host name.
> 
> Analysis:
> -------------
> 
> I have found that this is happening because in DDNS client code,
> before updating the server database with modified host name, client is
> checking whether a record with "new" host name exists.
> And server replies in negative for this ( which is correct ) and  we
> add a new record for the new host name. But previous entry with the old
> host name is never deleted from the server.
> 
> This check is done via "Prerequisite" record sent by the DDNS
> client. Since the prerequisite check fails, client doesn't send
> request for deletion of the "old" host name entry.
> 
> Forward zone file : /var/named/chroot/var/named/example.com.zone
> 
> 
> Could you kindly let me know if this behavior is correct to have
> multiple entries in the forward zone on change of host name.
> 
> ( Similar would be observed for reverse zone on change of IP Address
> i.e multiple IP point to same name. )
> 
> Thanks in advance,
> 
> With Regards,
> Nirav

	From the DNS perspective yes.  The DNS has done exactly
	what it was told to do.

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org