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Questions tagged [reverse-dns]

Reverse DNS lookup is the determination of a domain name that is associated with a given IP address using the Domain Name System (DNS) of the Internet.

Reverse DNS lookup or reverse DNS resolution (rDNS) is the determination of a domain name that is associated with a given IP address using the Domain Name System (DNS) of the Internet.

Computers use DNS to determine the IP address associated with a domain name. This process is also known as forward DNS resolution. Reverse DNS lookup is the inverse process, the resolution of an IP address to its designated domain name.

Forward-confirmed reverse DNS (FCrDNS), also known as full-circle reverse DNS, double-reverse DNS, or iprev, is a networking parameter configuration in which a given IP address has both forward (name-to-address) and reverse (address-to-name) Domain Name System (DNS) entries that match each other. This is the standard configuration expected by the Internet standards supporting many DNS-reliant protocols.

A FCrDNS verification can create a weak form of authentication that there is a valid relationship between the owner of a domain name and the owner of the network that has been given an IP address. While weak, this authentication is strong enough that it can be used for whitelisting purposes because spammers and phishers cannot usually by-pass this verification when they use zombie computers for email spoofing. That is, the reverse DNS might verify, but it will usually be part of another domain than the claimed domain name.

Forward Confirmed Reverse DNS

Reverse DNS.

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What's the command-line utility in Windows to do a reverse DNS look-up?

Is there a built-in command line tool that will do reverse DNS look-ups in Windows? I.e., something like w.x.y.z => mycomputername I've tried: nslookup: seems to be forward look-up only. host: doesn't exist dig: also doesn't exist. I…
alastairs
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What's the reverse DNS command line utility?

What's the command to find the name of a computer given its IP address? I always forget what this command is, but I know it exists in Windows and I assume it exists on the *nix command-line.
Peter Turner
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Multiple Reverse DNS Entries?

I'm a DNS noob, so here's a question: Can a server have multiple reverse DNS entries? Or does one IP address just resolve to one DNS name? Here is why I need this: I have a number of sites hosted on a server, as well as the mail for a number of…
Sam Schutte
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Do internet standards require reverse DNS for every device?

The requirements surrounding reverse DNS are confusing! People frequently talk about everything breaking if reverse DNS is not present, and that sounds scary. Even in cases where applications don't require reverse DNS, RFCs are frequently cited in…
Andrew B
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Has my ISP mangled my DNS reverse lookup record for a single static IP address?

I've taken on the task of running a small email server, and the world of spam makes it more challenging for an individual, as many MTAs are highly paranoid about accepting email. I think I've configured nearly everything that could be a problem…
StewLG
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Reverse DNS in a CIDR world

Reverse DNS seems to be strongly tied to class boundaries, what methods exist now that CIDR is the standard to delegate authority for a subnet? If multiple methods exist which one is best? Do you need to handle delegation differently depending on…
Zoredache
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How can this tool find out registered domains from an IP address?

This is one that I've never really known how to do, and it's been nagging me from time to time for years. I've read all I could find, including all the answers here. None of them gives a real answer to the question. So please read carefully before…
Neithan Max
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Is it good practice or too draconian to reject mails from mailservers with no RDNS

I've recently dropped SpamAssassin and am now basing spam rejection on DNSRBL's, grey-listing and other basic tests and I'm wondering whether I should also block hosts that don't have a valid RDNS matching the EHLO? If I do this, am I going to make…
Peter White
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Will adding a second SPF record mess up my DNS?

Will adding a second SPF record mess up my DNS, or will it be like adding an extra nameserver? (i.e. it only helps, not hurts)
Abraham Vegh
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PTR record (rDNS) for multiple domains on a shared IP address

I host multiple domains on a single IP address: cats.com A @ --> 10.20.30.40 A mail --> 10.20.30.40 MX @ --> mail dogs.com A @ --> 10.20.30.40 A mail --> 10.20.30.40 MX @ --> mail I need to set up a PTR record for the IP address. This is so…
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Reverse DNS - how to correctly configure for SMTP delivery

I started a new service and we need to send emails to our customers (new account confirms, etc). My server is known as prod01.bidrodeo.com and resolves to 97.107.134.38 . For reverse DNS, 97.107.134.38 resolves to prod01.bidrodeo.com . However,…
Krystian Cybulski
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Is it OK to use my public domain name as my internal AD domain name instead of using .local internally?

I am taking over a project and the local domain name is domain.com; they also have a website at domain.com. I have always used domain.local for AD, and am wondering if that is a best practice or is there a reason for not doing so. Running an…
Anthony Fornito
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Detect spammers on my server

I recently got one Undelivered Mail Returned to Sender while sending my newsletter to one of my 1500 customers. My website uses a double-opt-in procedure to make sure, the user explicitly want to receive my newsletter. The error message: smtp; 554…
koseduhemak
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Reverse DNS is not a valid hostname

I help a friend run a server, which includes a mail server. http://mxtoolbox.com reports that our reverse DNS is not a valid hostname. The reverse DNS currently points to domain.com. Should it point to hostname.domain.com? I have seen here that it…
ConnorJC
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How to force an ISP to remove false reverse DNS?

There is an IPv4 address (in a /8 managed by ARIN) that I have no control over which reverse resolves to a domain name which I registered. Someone used the IP address to run a scam, and it is resulting in negative publicity for my domain, so I would…
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