Dns updating zone serial


17-Nov-2017 19:39

Modern DNS server packages with sophisticated database back ends such as SQL servers and Active Directory allow administrators to make updates to the database in multiple places (such systems employ Multi-master replication), with the database back end's own replication mechanism handling the replication to all other servers.This paradigm simply does not match that of a single, central, monotonically increasing number to record changes, and thus is incompatible with zone transfer to a large extent.The portion of the database that is replicated is a zone.Zone transfer comprises a preamble followed by the actual data transfer.If the serial numbers are identical, the data in the zone are deemed not to have "changed", and the client may continue to use the copy of the database that it already has, if it has one.The actual data transfer process begins by the client sending a query (opcode 0) with the special query type AXFR (value 252) over the TCP connection to the server.Some clients check merely that the serial number supplied by the server is different from that known by the client, or non-zero.Other clients check that the serial number supplied by the server is within a given range of the serial number already known by the client.

Zone transfer operates in terms of "wire format" resource records, i.e.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.