I have a client that I am hosting DNS for and their ISP delegated part of a /24 block to my dns servers for reverse dns. So basically I have a block of x.x.x.64/27 delegated to my dns servers. I'm not sure of the syntax for the zone for a partial block. I did setup a full block for the full /24 block and locally reverse dns works for the IP addresses in question. However, inbound queries seem to fail since various tests (aol in particular) still fail externally. My problem, of course, is that most of the major ISPs will not accept mail from the locally hosted email server because the reverse dns query is failing.

Anyone have the syntax for a CIDR partial block reverse zone?



Please correct me If I am wrong, do you
mean to say that the ISP service from which you receive internet service doesnot accept mails from the Mail Server in your local network?
Well this could be because your ISP Service
is not recognizing the Mail Server in your local network.

The ISP Service must have the DNS enteries of your Mail Server in its DNS Server.
The forward lookup zone which converts fully qualified domain name into IP address and reverse lookup zone which does the reverse.

No, my ISP offers basic service. Basically, my client is buying a T1 from them with a /30 block for our gateway and theirs and a /27 block of static IPs to do with as we please. We are hosting an email server and a web server on that static block. In terms of the ISPs that were not accepting mail, it was every major ISP and they were rejecting us with the message "Reverse dns query failed, we require reverse dns to accept mail". So I called our isp to get that setup and they delegated the /27 to us instead. My question was how do I create that partial in-addr.arpa zone to host that /27.

In case anyone else runs up against this problem here is the solution:

Normally, to host say the reverse zone you would create a zone called 1.168.192.in-addr.arpa with PTR records inside for each host like so:

2 PTR somehost.somedomain.com. <------notice the trailing dot, important!!

To host a partial zone say, with hosts from 65-78 (network is 64, broadcast is 79) you would create a zone like this 64/ That zone is delegated by the owner of the full block to your dns servers. Inside the zone file you would create entries just like above, ie:

65 PTR email.somedomain.com. <-----again, notice trailing dot

This gave me fits since I have one internal master dns server that the public can't see and two slaves that get automatically updated with new zone via a script. Unfortunately, the name of the zone having a slash in it, broke that script and I ended up having to manually create this zone on my publicly facing IP addresses. Not that big a deal to have one manually configured zone, but I like to keep things standard.

So, everything is now working.