shell:$ nslookup -timeout=2 -retry=1 'twitter.us'
;; Got SERVFAIL reply from 1.1.1.1, trying next server
;; Got SERVFAIL reply from 8.8.8.8
Server:		8.8.8.8
Address:	8.8.8.8#53

** server can't find twitter.us: SERVFAIL