[SOLVED] Reverse DNS addr.arpa purpose

tripialos · 03-08-2016, 04:38 PM

Noob question incoming

Iv been reading a few articles abour Reverse DNS and PTR records but i still cant understand the logic behind the in.addr.arpa.

What is the puprose of the relevant domain? Since this is an ip-to-domain resolution, why is there a domain fit to the ip address? Wouldnt a table with the delegated ip ranges be enough?

Emerson · 03-09-2016, 08:54 AM

The purpose is to restrict spam, they want to be sure you are who you claim to be before accepting your mail. For instance, mail sent from infected Windows computers obviously does not have a valid PTR record.

Doug G · 03-09-2016, 08:11 PM

I suspect the actual in.addr.arpa name is necessary for DNS servers to operate on PTR records using normal zone lookups, rather than creating a separate protocol for PTR lookups.

In any case, valid PTR records are provided by your isp. I know verizon automatically created PTR records for my static FIOS ip's (and if I put an infected computer on my network it could certainly send spam with valid PTR records).

tripialos · 03-17-2016, 03:24 AM

I understood the whole PTR thing when i realized that in.addr.arpa is an actual domain/zone and as @Doug G stated, the same protocol is used to reverse the resolve. Hence why configuring a PTR zone in bind9 you have to reverse the ip address.