legend:
foe: rcode 1 - FORMERR - format error
srf: rcode 2 - SERVFAIL - server failure
nxd: rcode 3 - NXDOMAIN - no such domain
noi: rcode 4 - NOTIMPL - not implemented
ref: rcode 5 - REFUSED - refused
yxd: rcode 6 - YXDOMAIN - some name that ought not to exist, exists (rfc2136)