Servidores DNS Principal (mname) y Secundario (rname)
host: btclbs.com
class: IN
ttl: 21600
type: SOA
mname: ns-cloud-b1.googledomains.com
rname: cloud-dns-hostmaster.google.com
serial: 4
refresh: 21600
retry: 3600
expire: 259200
minimum-ttl: 300