A Valid domain name without TLD on internet
http://good
$ dig good
; <<>> DiG 9.8.3-P1 <<>> good ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 65133 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION: ;good. IN A
;; Query time: 3 msec ;; SERVER: 192.168.11.1#53(192.168.11.1) ;; WHEN: Mon Feb 19 12:13:28 2018 ;; MSG SIZE rcvd: 22
I works because most browsers try to add ".com" to an invalid domain name. And good.com is valid
$ dig good.com
; <<>> DiG 9.8.3-P1 <<>> good.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57755 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION: ;good.com. IN A
;; ANSWER SECTION: good.com. 19030 IN A 216.136.156.80
;; Query time: 4 msec ;; SERVER: 192.168.11.1#53(192.168.11.1) ;; WHEN: Mon Feb 19 12:14:05 2018 ;; MSG SIZE rcvd: 42
And http://good.com redirects after some jumps to http://us.blackberry.com/
As the parent said, browsers try to fix bad domains by themselves.
> $host good to find the Ip address of the server
NXDOMAIN. if you get something else, your DNS provider is injecting something.
$ host good
Host good not found: 2(SERVFAIL)
$ host good.com
good.com has address 216.136.156.80
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