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-   -   Reverse DNS: please little help (http://www.howtoforge.com/forums/showthread.php?t=49416)

gdavid 13th October 2010 20:00

Reverse DNS: please little help
 
Really I can't figure out how to set a reverse DNS for my servers.
Example: I want to reverse my public mail server (named mail.mycompany.com, IP 111.222.333.444)

I already have a correctly-working Zone for "mycompany.com." responding to "nslookup mail.mycompany.com"
Please can somebody explain to me (as if I were 5-yrs old ...)how to setup the reverse DNS name "mail.mycompany.com"?
Only this is missing to switch to MyDNS + MyDNSConfig!!!
Thanks in advance

g

edge 13th October 2010 20:18

You need to ask you ISP to set the reverse IP.

gdavid 14th October 2010 11:42

Thanks, edge. I already read the same answer to a post asking nearly the same question.
But until now I had to ask nothing to my ISP. We are currently running BIND as primary and backup DNS servers. When we have to set some reverse lookup we just add an entry to the zzz-qqq.uuu.yyy.xxx.IN-ADDR.ARPA. where zzz-qqq is the IP ranges assigned from the ISP to our subnet.
An example for that entries is:

58 IN PTR mail.mydomain.com.
59 IN PTR ftp.mydomain.com.
where 58 and 59 are the last part of the public IP address of the mail and ftp servers.
We have not a /24 subnet, so maybe the first step in reverse lookup is done by the ISP pointing to our currently running DNS (BIND) and then is reversed by us.
This can explain the problem: actually MyDNS is still in test, so is not "declared" to the internet.
But if I execute
#dig @xxx.yyy.zzz.fff -x xxx.yyy.zzz.qqq
(where xxx.yyy.zzz.fff is the IP our new-MyDNS Server and xxx.yyy.zzz.qqq is the IP we want to reverse), we should work around that problem, because we asking directly to our new server to reverse-lookup the IP xxx.yyy.zzz.qqq
Whre am I wrong?

In any case, suppose we have a /24 subnet: how can we, within MyDNSConfig, setup the reverse DNS for our servers? How can we "declare" that xxx.yyy.zzz.qqq is for mail.mydomain.com and xxx.yyy.zzz.hhh is for ftp.mydomain.com ?

I found the answer by myself (supposing we have a /24 subnet xxx.yyy.zzz.0-255):
in MyDNSConfig just create a new zone named "zzz.yyy.xxx.in-addr.arpa.", then add PTR records inserting as "Name" the last number part of the IP of the server you want to reverse (ie "qqq") and inserting in the Canonical Hostname field the complete hostname (ie "mail.mydomain.com.")

Now, if my ISP reverse only a part of the /24 subnet, maybe him reverse something like "aaa-fff.zzz.yyy.xxx.in-addr.arpa.", so I have to change my zone name from "zzz.yyy.xxx.in-addr.arpa." to "aaa-fff.zzz.yyy.xxx.in-addr.arpa."
I will try if it works.

Thanks for pointing me in the right direction
g

gdavid 25th October 2010 13:59

Update:

No, It doesn't work. The problem is the syntax for reverse DNS lookup forwarded by our ISP.
That syntax ( aaa/fff.zzz.yyy.xxx.in-addr.arpa. ) is not accepted by MyDNS when you create the zone.
We are now waiting for our ISP to modify (if possible) the syntax of the reverse DNS request.

gdavid 25th October 2010 14:25

Update:

The syntax problem with "/" for subnets seems a problem of MyDNSConfig, and NOT of MyDNS. In fact, when modifying directly the table dns_soa in MyDNS Database, inserting a zone "aaa/fffzzz.yyy.xxx.in-addr.arpa." is obviously possible and this works with the IPS adopting that syntax for subnets reverse DNS requests.

Now the problem is that you have to modify this zone from the DB. If MyDNSConfig developers can modify the code, it would be nice :)
Thanks
g

gdavid 5th November 2010 19:28

Ok. I modified the code by myself doing the following:
- Locate the file "dns_soa.tform.php" in your web applications path of mydnsconfig
- Modify the line:
'regex' => '/^[\w\.\-]{2,64}\.[a-zA-Z]{2,10}[\.]{0,1}$/',
to:
'regex' => '/^[\w\.\-\/]{2,64}\.[a-zA-Z]{2,10}[\.]{0,1}$/',

Thath's all!
Enjoy


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