topic Re: Reverse DNS lookup in Operating System - Linux

Reverse DNS lookup

'chris' — Mon, 30 May 2005 09:34:10 GMT

hi

What kind of problems could have a name server (DNS server)
or a webserver if his Reverse DNS lookup doesn't work.

kind regards
chris

Re: Reverse DNS lookup

Alexander Chuzhoy — Mon, 30 May 2005 09:37:55 GMT

does the server has reverse lookup zone?
if so:
attach /etc/named.conf and the file of reverse lookup zone

Re: Reverse DNS lookup

Gopi Sekar — Mon, 30 May 2005 10:25:19 GMT

simple:

all network establishing request to that server will be delayed by minutes.

the server will try to reverse lookup the connection query to find out the server name, if it is not able to find out depending on the security of the application it either discards the connection or times out and accepts it

Regards,
Gopi

Re: Reverse DNS lookup

Alexander Chuzhoy — Mon, 30 May 2005 10:38:16 GMT

the nslookup utility and such won't work.

Re: Reverse DNS lookup

Steven E. Protter — Mon, 30 May 2005 21:11:45 GMT

It usually is the format of the reverse lookup records. I'm going to attach a proper example for you.

It could be the reverse zone is not listed in /etc/named.conf

SEP

Re: Reverse DNS lookup

Suraj Singh_1 — Wed, 01 Jun 2005 06:02:36 GMT

Hi,

Any network application using tcp wrapper (such as telnet) will experience a delay while trying to establish a connection.

Apart from that, when you do nslookup, your DNS server's name would be 'unknown' since the IP od DNS server will not have a PTR record.

Regards

Re: Reverse DNS lookup

Rick Garland — Wed, 01 Jun 2005 07:58:31 GMT

There will be some applications that will not work, or will not work well. Some applications have a higher dependence on lookups by name as opposed to IP address.

Re: Reverse DNS lookup

Bejoy C Alias — Thu, 02 Jun 2005 08:13:51 GMT

can u be more clear...
u mean , ur server's ip doesnt have a reverse dns entry OR ur server cannot do any other ips reverse dns lookup ?

Re: Reverse DNS lookup

'chris' — Thu, 02 Jun 2005 13:12:38 GMT

It's not my server,
I mean every server without reverse DNS lookup,
for example:

bsd# host 212.244.86.18
Host not found.

I think some mail servers will deny the mails from the servers without reverse DNS lookup.

Re: Reverse DNS lookup

Steven E. Protter — Thu, 02 Jun 2005 17:22:23 GMT

To deliver mail to aol and me, you must have reverse lookup records.

You don't need them for every server. You need them for the ip address that is actually being used to send the mail.

If the mail from server1 is relayed by relay1, the IP address on the public Internet that does the actualy work of transferring the mail to other servers needs a reverse lookup address for that IP address.

SEP

Re: Reverse DNS lookup

Bejoy C Alias — Sat, 04 Jun 2005 02:28:51 GMT

If a server is not having reverse entry and it is used for sending mails to external sites directly , then some of the servers to which u r sending mails will reject ur mails. This for a security purposes mainly for rejecting spam mails... . Again if the server is not having a reverse dns entry it may create some pblms for applications where there will be some access control mechanisms to prevent connections from some particular host names or ips . In this case if the server is allowed to connect only from say host1.com with ip 1.2.3.4 , the actual connections will be using ips , so the server will check the the reverse dns of 1.2.3.4 to find out whether it is from host1 or not..if it cannot do this reverse lookup , then it may create pblms... I think there wont be any pblm for web servers for reverse dns..