Dns updating zone serial Windsor hook up girls
The preamble comprises a lookup of the Start of Authority (SOA) resource record for the "zone apex", the node of the DNS namespace that is at the top of the "zone".The fields of this SOA resource record, in particular the "serial number", determine whether the actual data transfer need to occur at all.Though servers can send a NOTIFY message to clients (that they have been informed about) whenever a change to the zone data has been made, the scheduling of zone transfers is entirely under the control of the clients.Clients schedule zone transfers initially, when their databases are empty, and thereafter at regular intervals, in a pattern controlled by the values in the "refresh", "retry", and "expire" fields in the SOA resource record of the zone apex.
The client requesting a zone transfer may be a slave server or secondary server, requesting data from a master server, sometimes called a primary server.The client compares the serial number of the SOA resource record with the serial number in the last copy of that resource record that it has.If the serial number of the record being transferred is greater, the data in the zone are deemed to have "changed" (in some fashion) and the slave proceeds to request the actual zone data transfer.However, since TCP can be used for normal DNS transactions, as well as for zone transfer, other zone transfer clients perform the SOA lookup preamble over the same TCP connection as they then (may) perform the actual data transfer.These clients open the TCP connection to the server before they even perform the preamble. Incremental zone transfer differs from full zone transfer in the following respects: Zone transfer is entirely client-initiated.
Modern DNS server packages with sophisticated database back ends often will create a "shim" serial number, simulating the existence of a single central place where updates are made, but this is at best imperfect.