PTR records serve as as a reverse IP-address display in the host name.
Example: PTR record (or Reverse DNS) translates the domain name ns.cloudhost.lv in IP-address 18.104.22.168. And it also allows the address 22.214.171.124 return to ns.cloudhost.lv. Some hosters indicate PTR record for their pages for example:
$ nslookup 126.96.36.199 Server: 188.8.131.52 Address: 184.108.40.206#53 Non-authoritative answer: 220.127.116.11.in-addr.arpa name = web.cloudhosting.lv.
$ nslookup 18.104.22.168 ns.cloudhost.lv Server: ns.cloudhost.lv Address: 22.214.171.124#53 126.96.36.199.in-addr.arpa name = web.cloudhosting.lv.
Basically these records is used as a spam filter. Spammers often forge domain names to send e-mail, which generally will not have a proper PTR record created from the DNS. The presence of reverse Reverse DNS - one of the basic requirements of many spam filters. His absence could lead to blocking of emails. Also, when a web analysis and the analysis of Internet traffic using a reverse search Reverse DNS, to find out which service providers in your visitors.
For PTR records do not have specific technical requirements. However, with an increase in unwanted electronic messages (spam), they are necessary for some security schemes.
Exactly therefore Most of Providers For PTR records applies the following rules:
In other words, we must able to take IP-address, look it PTR-record, find an A record for that host and return the IP-address.
$ host -a cloudhosting.lv Trying cloudhosting.lv ;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;cloudhosting.lv. IN ANY ;; ANSWER SECTION: cloudhosting.lv. 14397 IN A 188.8.131.52 cloudhosting.lv. 21597 IN NS ns2.cloudhost.lv. cloudhosting.lv. 21597 IN NS ns.cloudhost.lv. cloudhosting.lv. 14397 IN MX 5 mailhost.energy.lv. cloudhosting.lv. 14397 IN TXT v=spf1 a mx ip4:184.108.40.206 ?all Received 221 bytes from 220.127.116.11#53 in 18 ms
$ nslookup -type=soa cloudhosting.lv Server: 18.104.22.168 Address: 22.214.171.124#53 Non-authoritative answer: cloudhosting.lv origin = ns.cloudhost.lv mail addr = dns.energy.lv.lv serial = 2013090901 refresh = 86400 retry = 7200 expire = 604800 minimum = 86400
$ nslookup -type=any cloudhosting.lv Server: 126.96.36.199 Address: 188.8.131.52#53 Non-authoritative answer: cloudhosting.lv origin = ns.cloudhost.lv mail addr = dns.energy.lv.lv serial = 2013090901 refresh = 86400 retry = 7200 expire = 604800 minimum = 86400 Name: cloudhosting.lv Address: 184.108.40.206 cloudhosting.lv nameserver = ns2.cloudhost.lv. cloudhosting.lv nameserver = ns.cloudhost.lv. cloudhosting.lv mail exchanger = 5 mailhost.energy.lv. cloudhosting.lv text = v=spf1 a mx ip4:220.127.116.11 ?all