$ dig -x 104.18.104.234

; <<>> DiG 9.11.3-1ubuntu1.7-Ubuntu <<>> -x 104.18.104.234
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 23441
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: bf8760844990caeb8aa284455cc6623e4d537f1b83fc0973 (good)
;; QUESTION SECTION:
;234.104.18.104.in-addr.arpa.	IN	PTR

;; Query time: 111 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Sun Apr 28 19:32:30 PDT 2019
;; MSG SIZE  rcvd: 84