ISPconfig - Classless Reverse DNS Delegation

Sonora Communications, Inc.

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ISPconfig - Classless Reverse DNS Delegation

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These are only some quick notes pertaining to the fairly new phenomenon of 'Classless Reverse DNS Delegation' as it concerns ISPconfig.

The first time we ran into this issue was when a customer whose DNS we were hosting got a new T1 Internet connection from AT&T. Now, AT&T, being the smart organization they are, decided to let customers handle their own reverse DNS or charge them for the privilege of AT&T doing it. Then they also attached a few other 'rules'...

Here is an example of the e-mail message AT&T sent to the customer:

Subject: RE: Reverse DNS/ PTR Record

This is to confirm the following IP BLock of 168/ is delegated to the nameservers of and

Takes approx 24 hours to fully cache throughout the network.

Note that in this example, the IP provider issued this small subnet of IP addresses:

Anyway, ISPconfig automatically creates reverse zones when you add PTR records. The only problem is the 'classless delegation' part. The reverse zones ISPconfig creates are apparently for the (older) standard Class A, B or C addressing schemes which don't work for smaller sites or smaller ISPs.

In our case, we found that we could simply create a new zone in named.conf and point it at the zone file already maintained by ISPconfig.

vi /var/named/chroot/var/named/chroot/etc/named.conf

and add at the bottom:

zone "168/" {   
        type master;
        file "";

In this case, the "file" line points to the preexisting file created by ISPconfig in /var/named/chroot/var/named/.


Last Updated on Thursday, 26 February 2009 14:30