IPTOOL TR My IP

DNS

Reverse DNS: PTR and FCrDNS

IP to PTR: FCrDNS, in-addr.arpa / ip6.arpa. Paste a URL or IP:port.

IP address
Example IPs

https://8.8.8.8 or 1.1.1.1:443 is accepted. IPv6 may be in brackets. PTR is published by the IP owner (ISP/host).

Queries leave from this Linux server, not your ISP DNS. Free. Cached answers can differ for a short time.

PTR and FCrDNS

Reverse DNS maps an IP to a hostname. Mail egress wants PTR plus a forward match (FCrDNS). Websites do not require it.

IP / topic PTR / zone Note
8.8.8.8 dns.google Google Public DNS. A resolver, not a mail host.
1.1.1.1 one.one.one.one Cloudflare 1.1.1.1. IPv6 twin is 2606:4700:4700::1111.
9.9.9.9 dns9.quad9.net Quad9. May filter malicious names.
IPv4 in-addr.arpa Octets reversed: 8.8.8.8 → 8.8.8.8.in-addr.arpa.
IPv6 ip6.arpa 32 hex nibbles reversed. Type the address as usual.
Mail FCrDNS The PTR hostname must A/AAAA back to the same IP. Gmail/Outlook expect this.

What does reverse DNS show?

PTR names the hostname for an IP; it is the reverse of A/AAAA. This tool takes the address you type (a pasted URL or IP:port is stripped to the IP) and asks the system resolver. The card highlights the hostname, the in-addr.arpa / ip6.arpa zone, and FCrDNS.

Missing PTR is not a web error. On a mail egress IP it raises suspicion at Gmail and Outlook. The record is set by the IP-block owner (ISP or host), not in your domain DNS panel.

Chips, IPv4 and IPv6

Chips for 8.8.8.8, 1.1.1.1, 9.9.9.9, OpenDNS and IPv6 fill the box. This connection’s IP can be selected too. https://1.1.1.1/ or [2606:4700:4700::1111]:443 is accepted.

The IPv4 zone reverses octets. IPv6 reverses 32 hex nibbles. Type the address as usual; do not build ip6.arpa by hand.

FCrDNS and mail

Forward-confirmed rDNS: the PTR name must A or AAAA back to the same IP. The card shows green when it matches, amber when it does not. Several PTRs are allowed; for mail prefer one that matches FCrDNS.

A dynamic home IP often has a generic ISP PTR without FCrDNS. On a static server IP, ask the provider. SPF/DKIM do not replace PTR.

Who publishes it?

in-addr.arpa and ip6.arpa sit under the IP allocation (RIR / ISP). Changing your A record does not change PTR. For reputation also use the blacklist tool.

The query leaves from this Linux host. It may not match your ISP cache. The rate limit cuts off frequent queries.

Frequently asked questions

Will mail still send without PTR?

Sometimes, but large providers treat it as suspicious. Ask your provider for PTR on a static IP.

Where do I set PTR?

The IP-block owner (host or ISP) sets it. Your domain DNS panel cannot publish PTR.

What is forward-confirmed rDNS?

The PTR hostname must resolve back to the same IP. Recommended for mail.

How is IPv6 PTR queried?

Enter the address as usual; the tool builds the ip6.arpa name from reversed hex nibbles.

Can there be several PTRs?

Technically yes; for mail prefer one record that matches FCrDNS.