At my company (getstream.io) we've been having issues when resolving our domains randomly. After some more investigation it seems some .io nameservers are returning bad results. Specifically ns-a2.io and ns-a4.io. A correct result for crates.io looks like this:
$ dig crates.io @ns-a1.io +norecurse
; <<>> DiG 9.11.2 <<>> crates.io @ns-a1.io +norecurse
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18874
;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 3,
ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;crates.io. IN A
;; AUTHORITY SECTION:
crates.io. 86400 IN NS dns3.easydns.ca.
crates.io. 86400 IN NS dns1.easydns.com.
crates.io. 86400 IN NS dns2.easydns.net.
;; Query time: 83 msec
;; SERVER: 194.0.1.1#53(194.0.1.1)
;; WHEN: Wed Sep 20 15:33:13 CEST 2017
;; MSG SIZE rcvd: 127
A bad one looks like the following:
dig crates.io @ns-a4.io +norecurse
; <<>> DiG 9.11.2 <<>> crates.io @ns-a4.io +norecurse
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 43223
;; flags: qr aa; QUERY: 1, ANSWER: 0, AUTHORITY: 1,
ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;crates.io. IN A
;; AUTHORITY SECTION:
io. 900 IN SOA a0.nic.io. noc.afilias-nst.info. 1497256201 10800 3600 2764800 900
;; Query time: 10 msec
;; SERVER: 74.116.179.1#53(74.116.179.1)
;; WHEN: Wed Sep 20 15:34:59 CEST 2017
;; MSG SIZE rcvd: 105
This has happened last year as well, so I wouldn't recommend running something important on a .io domain: https://news.ycombinator.com/item?id=12813065
