[dns-operations] OT: NXDOMAIN / public resolvers and zen.spamhaus.org

[Matthew Walker]

I recently noticed after switching my forwarders to public resolvers, 
that zen.spamhaus.org was returning NXDOMAIN.

So, I began some basic testing, and it seems both GoogleDNS and Level3 
are returning NXDOMAIN when using a zen.spamhaus.org test domain. 
OpenDNS appears to be resolving zen.spamhaus.org without any issues.

# google public dns
$ host 107.178.203.192.zen.spamhaus.org 8.8.8.8
Host 107.178.203.192.zen.spamhaus.org not found: 3(NXDOMAIN)

$ host 107.178.203.192.zen.spamhaus.org 8.8.4.4
Host 107.178.203.192.zen.spamhaus.org not found: 3(NXDOMAIN)

# level3 dns
$ host 107.178.203.192.zen.spamhaus.org 4.2.2.1
Host 107.178.203.192.zen.spamhaus.org not found: 3(NXDOMAIN)

# opendns
$ host 107.178.203.192.zen.spamhaus.org 208.67.222.222
107.178.203.192.zen.spamhaus.org has address 127.0.0.2

$ host 107.178.203.192.zen.spamhaus.org 208.67.220.220
107.178.203.192.zen.spamhaus.org has address 127.0.0.2

So a word of warning if you do use public resolvers, that it might have 
unexpected results.