Dig is a DNS lookup utility provided by ISC. This page is a simple web interface for dig.
$ dig 221.4.96.4 PTR ; <<>> DiG 9.11.3-1ubuntu1.3-Ubuntu <<>> 221.4.96.4 PTR ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 53582 ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;221.4.96.4. IN PTR ;; AUTHORITY SECTION: . 82454 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2018121002 1800 900 604800 86400 ;; Query time: 8 msec ;; SERVER: 139.162.69.5#53(139.162.69.5) ;; WHEN: Mon Dec 10 22:35:25 UTC 2018 ;; MSG SIZE rcvd: 114