DNS PTR Problem

[Cogen]

Hello, I have a DNS issue regarding the reverse lookup on my server, and I don't know if I understand how it works enough to fix the problem.
When I do a reverse lookup on my server's IP I get this feedback (from dnsstuff.com)..

Asks a few root server and comes up with ns2.serverbeach.com

Asking ns2.serverbeach.com. for 20.34.###.###.in-addr.arpa PTR record: Reports server1.mydomain.com.

Answer:
###.###.34.20 PTR record: server1.mydomain.com. [TTL 86400s] [A=None] *ERROR* A record does not point back to original IP.

----
I don't know why it says that the A record does not point back to the original IP? If I ping server1.mydomain.com, it goes to the same IP address I used in the search???

 

[ChrisAC]

If you give us the IP address then we can check it.

Chris.

**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[Cogen]

Thanks for the help iproute, but I think I figured it out. The reverse lookup is working now.

 

[scjlin]

Cogen,

I having the same problem. *ERROR* A record does not point back to original IP. How did you made it to work.

Thanks,

sl

 

[ChrisAC]

You create a pointer record that maps to the forward record. eg.

Forward DNS ...

domain.com IN MX 10 mail.domain.com
mail.domain.com IN A 100.200.300.400

Reverse DNS ...

400.300.200.100.in-addr.arpa IN PTR mail.domain.com

Or, how about a real life example, tek-tips styley!!

tek-tips.com. 3600 MX 0 mail.tecumsehgroup.com.

mail.tecumsehgroup.com. 3600 A 216.45.19.20

20.19.45.216.in-addr.arpa. 86400 PTR mail.tecumsehgroup.com

In your case obviously the forward and reverse don't match.

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[scjlin]

Thanks for prompt reply.
There is another question. The error A record shown from dnsstuff is indicated a 216.x.y.z network. However my network is 208.x.y.z, and I check my dns server there is no such record or zone indicated to 216 network. And yes, the reverse DNS lookup is point to my DNS server from dnsstuff.

Another problem is my internet domain is different than my internal domain structure. My outside domain is abc.com. However internal domain is running as a-abc.com

Thanks


sl

 

[ChrisAC]

What's your external domain name?

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[scjlin]

Let’s use Tek-tips as example. My external domain name would be tek-tips.com (208.x.y.z). However my internal domain name is tektips.com which was taken by someone else with 216.x.y.z ip address.

Asking ns2.tek-tips.com. for z.y.x.208.in-addr.arpa PTR record: Reports mail.tektips.com.

Answer:
208.x.y.z PTR record: mail.tektips.com. [TTL 458s] [A=216.x.y.z] *ERROR* A record does not point back to original IP.


Actually I believed all my dns reverse lookup records are not working at all! I tried all the record in the reverse lookup zones though dnsstuff.com most likely it will return no PTR records associated on my dns server. I sure I have defined correct PTR records in the zones already. Sorry for security purpose I can’t post my IP and domain name in public place.

Many thanks,



sl

 

[ChrisAC]

Okay, email me your domain name then and I will check it. Without that I can't be of any more help.

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[Cogen]

scjlin .. in my case it was a pretty easy fix. I had the PTR record pointing to server1.mydomain.com. The problem is that server1.mydomain.com is just a CNAME pointing to server.mydomain.com. You cannot point a PTR record to a CNAME, it must be pointed to an A record (I think). Therefore, after changing the PTR record to server.mydomain.com everything started to work great.