Setting up reverse DNS for a /25 block of IPs

Question

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";
};

See: http://serverfault.com/questions/22743/reverse-dns-in-a-cidr-world — Zoredache, Sep 20 '11 at 23:00

Shane Madden · Accepted Answer · 2011-09-20T22:01:30.357

3

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

edited Sep 20 '11 at 22:01

answered Sep 20 '11 at 21:50

Shane Madden

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Dang, Shane. You're a smart guy. I wish I had your knowledge when I was your age. In fact, I wish I had your knowledge now. At the least, it gives me something to work toward. – joeqwerty Sep 20 '11 at 22:21
I don't actually control the whole /24, just the ips .128-255. Would I just create a reverse for the /24 anyway, forwarding like you've shown? – Devar-TTY Sep 20 '11 at 22:29
@joeqwerty Nah, I'm just winging it. Flattery! ;) We've all got our own expertise to contribute, which makes this community as good as it is. – Shane Madden Sep 20 '11 at 22:32
@rkalajian The owner of the IP block needs to delegate control to you; they'd be the ones to enter the config I've posted above into their zone for the /24. When a client looks for reverse DNS for those entries, they will be directed to the name servers specified by the owner of the IP block (which must be a /24 or greater); the owner of that block would then need to delegate those addresses to you. – Shane Madden Sep 20 '11 at 22:36
My colo has it delegated, but with dash notation. I fixed it on my end, and the damn rDNS still doesn't work. – Devar-TTY Sep 22 '11 at 13:42
Got it! There ended up being a mistype in one of the configs. – Devar-TTY Sep 23 '11 at 17:57

Setting up reverse DNS for a /25 block of IPs

1 Answers1