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DNS, reverse lookup and PTR records

Posted on 2014-04-22
Medium Priority
Last Modified: 2014-05-12
Question: Secure services in your network require reverse name resolution to make it more difficult to launch successful attacks against the services. To set this up, you configure a reverse lookup zone and proceed to add records. Which record types do you need to create?
Answer: PTR Records

I setup small business 2003 which comes with exchange built in for client once. Before my arrival he said everytime he would send an email to an AOL email address he would recieve a  bounce back message.

I then read on the internet that I have to create a PTR record - and that can only be done by the broadband company. I then left the company and never understood the whole thing.

Can some one explain what exactly a PTR record is? what is it so necessary?
Question by:Ikky786
LVL 84

Accepted Solution

Dave Baldwin earned 668 total points
ID: 40014161
Below are the DNS records for Microsoft.com.  You can see that each of the 'nameservers' and the main 'microsoft.com' site have PTR records associated with them.  It is basically a way to cross check that the remote IP is valid for the domain.
1	microsoft.com	NS	ns5.msft.net		Answer	
2	microsoft.com	NS	ns1.msft.net		Answer	
3	microsoft.com	NS	ns2.msft.net		Answer	
4	microsoft.com	NS	ns3.msft.net		Answer	
5	microsoft.com	NS	ns4.msft.net		Answer	
6	microsoft.com	MX	microsoft-com.mail.protection.outlook.com	Preference: 10	Answer	
7	microsoft.com	A	microsoft.com		Answer	
8	microsoft.com	A	microsoft.com		Answer	
9	microsoft.com	CNAME			Error 9501: No records found for given DNS query.		
10	microsoft.com	SOA	ns1.msft.net	Admin: msnhst.microsoft.com, Default TTL: 3600, Expire: 2419200, Refresh: 300, Retry: 600, Serial: 2014042103	Answer	
11	microsoft.com	TEXT			v=spf1 include:_spf-a.microsoft.com include:_spf-b.microsoft.com include:_spf-c.microsoft.com include:_spf-ssg-a.microsoft.com include:spf-a.hotmail.com ip4: ip4: ip4: ip4: ip4: ~all	Answer	
12	microsoft.com	TEXT			FbUF6DbkE+Aw1/wi9xgDi8KVrIIZus5v8L6tbIQZkGrQ/rVQKJi8CjQbBtWtE64ey4NJJwj5J65PIggVYNabdQ==	Answer	
13	PTR	ns5.msft.net		Answer	
14	PTR	ns1.msft.net		Answer	
15	PTR	ns2.msft.net		Answer	
16	PTR	ns3.msft.net		Answer	
17	PTR	ns4.msft.net		Answer	
18	PTR	mail-bl24215.inbound.protection.outlook.com		Answer	
19	PTR	00001001.ch		Answer	

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LVL 17

Assisted Solution

by:Sajid Shaik M
Sajid Shaik M earned 668 total points
ID: 40014253
there is 2 things..

one is local Reverse dns which works on your local network...

the second thing is External which is done by ISP and DNS service provicer... where u publish you external DNS name...

so ask you service provider to create reverse dns entry for your External domain name

and check in the external DNS setting about the PTR record

all the best
LVL 19

Assisted Solution

alextoft earned 664 total points
ID: 40014818
If you imagine a DNS "A" record as allowing you to resolve mail.domain.com to, a PTR record is the reverse; it allows you to resolve to mail.domain.com

Just like a domain name has "NS" (nameserver) records attached to it which tell clients where to go to resolve hostnames in domain.com so do IP blocks. It's usually used as an anti-spam technique - checking that the server has a PTR record which ties it to the domain it's performing email services on behalf of, and/or that the A and PTR records resolve to each other.

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