---
title: "rDNS"
description: "rDNS (reverse DNS) is a lookup that maps an IP address back to a hostname. Learn about the PTR record, the in-addr.arpa zone and its importance for email."
url: "https://nodea.io/en/glossary/rdns-reverse-dns"
lang: "en"
updated: "2026-07-13"
---

# rDNS

> rDNS (reverse DNS) is a reverse DNS lookup that resolves an IP address to its associated hostname, the opposite of the standard name-to-address resolution.

**rDNS** (reverse DNS) is a [DNS](https://nodea.io/en/glossary/dns) lookup that works the opposite way to a standard one: instead of resolving a domain name into an IP address, it maps an IP address back to its associated hostname. Where forward DNS answers "what address does *nodea.pl* have?", rDNS answers "what name is behind the address 203.0.113.10?".

## How rDNS works

Reverse lookups use a special namespace, *in-addr.arpa* (for IPv4) and *ip6.arpa* (for IPv6). The key elements are:

- **PTR record** — this is what performs the IP-to-name mapping; it is the reverse counterpart of the [A record](https://nodea.io/en/glossary/a-record) (see the [PTR record](https://nodea.io/en/glossary/ptr-record)).
- **Reversed address notation** — the IP is written with its octets in reverse order plus the *.in-addr.arpa* suffix, e.g. 10.113.0.203.in-addr.arpa for 203.0.113.10.
- **Zone delegation** — control over the reverse zone belongs to whoever manages the address block (the IP provider), not the domain owner.

For rDNS to be considered trustworthy, *forward-confirmed reverse DNS* (FCrDNS) should hold — the name from the PTR record, when checked forward, must resolve back to the same IP.

## rDNS in practice

Reverse DNS has several important uses:

1. **Email** — [SMTP](https://nodea.io/en/glossary/smtp) servers verify the sender's PTR record; correct rDNS is a condition for good [deliverability](https://nodea.io/en/glossary/email-deliverability) and avoiding a spam classification.
2. **Logs and diagnostics** — network tools show hostnames instead of raw addresses, easing traffic analysis.
3. **Security** — some systems only accept connections from hosts with valid, consistent rDNS.

When running your own mail server on a VPS, setting the PTR record with the IP operator is one of the first steps that determine whether messages get delivered.

### What is an rDNS record needed for?

The main use is email. Receiving servers check whether the sender's IP has a valid PTR record pointing to its domain. Missing or inconsistent rDNS is a strong spam signal — messages may land in junk or be rejected outright.

### Who sets an rDNS record?

The PTR record for an IP is configured by the owner of the address block — usually the hosting, VPS or internet provider. You cannot set it in a domain's standard DNS panel; you must request it from the operator that manages the IP.

## Related

- [DNS](https://nodea.io/en/glossary/dns)
- [PTR record](https://nodea.io/en/glossary/ptr-record)
- [SMTP](https://nodea.io/en/glossary/smtp)
- [A record](https://nodea.io/en/glossary/a-record)
- [Deliverability](https://nodea.io/en/glossary/email-deliverability)

---

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