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Reverse DNS lookup

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'chris'
Super Advisor

Reverse DNS lookup

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


10 REPLIES
Alexander Chuzhoy
Honored Contributor

Re: Reverse DNS lookup

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

Re: Reverse DNS lookup


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

Never Never Never Giveup
Alexander Chuzhoy
Honored Contributor

Re: Reverse DNS lookup

the nslookup utility and such won't work.
Steven E. Protter
Exalted Contributor

Re: Reverse DNS lookup

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
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Suraj Singh_1
Trusted Contributor

Re: Reverse DNS lookup

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
What we cannot speak about we must pass over in silence.
Rick Garland
Honored Contributor

Re: Reverse DNS lookup

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.
Bejoy C Alias
Respected Contributor

Re: Reverse DNS lookup

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 ?
Be Always Joy ......
'chris'
Super Advisor

Re: Reverse DNS lookup

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.

Steven E. Protter
Exalted Contributor
Solution

Re: Reverse DNS lookup

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
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Bejoy C Alias
Respected Contributor

Re: Reverse DNS lookup

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..
Be Always Joy ......