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Devar-TTY
Asked: 2011-09-21 13:44:50 +0800 CST

Setting up reverse DNS for a /25 block of IPs

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I've currently got a block of IPs that go from xxx.xxx.xxx.128/25

Here's my current rDNS setup:

$TTL 12h
$ORIGIN 128/25.xxx.xxx.xxx.IN-ADDR.ARPA.

@       IN      SOA     ns1.domain.com. hostmaster.domain.com. (

                        2011092003      ; serial number
                        2h              ; refresh
                        1h              ; retry
                        2w              ; expire
                        1h      )       ; negative TTL

        IN      NS      ns1.domain.com.
        IN      NS      ns2.domain.com.

130       IN        PTR        mail.otherdomain.com.

It doesn't seem to be working properly. I've got it setup in named.conf like so:

zone "128/25.xxx.xxx.xxx.in-addr.arpa" {
    type master;
    file "master/128-25.xxx.xxx.xxx.in-addr.arpa";
};
domain-name-system bind ip-address reverse-dns

1 Answers

  1. Best Answer

    RFC2317 delegations aren't typical zones, clients don't know how to find them during a lookup; there will need to be a "delegation" (it's not a real delegation, as it's not really working inside the hierarchy of DNS) in the zone for the /24 sending every address in the /25 to your name server via a CNAME to the 128/25.x.x.x.in-addr-arpa. zone.

    Something like this in the /24's zone:

    128/25    IN    NS       your.server.here.

128       IN    CNAME    128.128/25
129       IN    CNAME    129.128/25
...
254       IN    CNAME    254.128/25
255       IN    CNAME    255.128/25
    • 3