The other authoritative servers, the slave servers (also known as secondary servers) - load - the zone contents from another server using a replication process - known as a zone transfer. Typically the data - are - transferred directly from the primary master, but it is also - possible - to transfer it from another slave. In other words, a slave server - may itself act as a master to a subordinate slave server. + load the zone contents from another server using a replication + process known as a zone transfer. + Typically the data are transferred directly from the primary + master, but it is also possible to transfer it from another + slave. In other words, a slave server may itself act as a + master to a subordinate slave server. +
++ Periodically, the slave server must send a refresh query to + determine whether the zone contents have been updated. This + is done by sending a query for the zone's SOA record and + checking whether the SERIAL field has been updated; if so, + a new transfer request is initiated. The timing of these + refresh queries is controlled by the SOA REFRESH and RETRY + fields, but can be overrridden with the + max-refresh-time, + min-refresh-time, + max-retry-time, and + min-retry-time options. +
++ If the zone data cannot be updated within the time specified + by the SOA EXPIRE option (up to a hard-coded maximum of + 24 weeks) then the slave zone expires and will no longer + respond to queries.
@@ -599,6 +616,6 @@ -BIND 9.12.0b1
+BIND 9.12.0b2