When querying a particular address, dig as run against the resolvers listed in /etc/resolv.conf will return NXDOMAIN nice and quickly where host will take a while.
$ dig @<resolver> 184.108.40.206.in-addr.arpa ptr ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 <<>> @<resolver>220.127.116.11.in-addr.arpa ptr ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 40000 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;18.104.22.168.in-addr.arpa. IN PTR ;; Query time: 1 msec ;; SERVER: <resolver>#53(<resolver>) ;; WHEN: Wed Oct 22 16:08:38 2014 ;; MSG SIZE rcvd: 44
But much slower in host...
$ time host 22.214.171.124 <resolver> ;; connection timed out; no servers could be reached real 0m12.007s user 0m0.001s sys 0m0.007s
Why does host take so long to come up with the same answer?