The internet class is assumed if class is not supplied.
The ttl is ignored, and is only allowed for compatibility.
The MNAME field of that zone's SOA record will identify the master server for that zone.
The prerequisite condition gets the name server to check that there are no resource records of any type for nickname. If this name does not exist, a CNAME for it is added.When no local statement is provided, nsupdate will send updates using an address and port chosen by the system.port can additionally be used to make requests come from a specific port.The -d option makes nsupdate operate in debug mode.This provides tracing information about the update requests that are made and the replies received from the name server.