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Stub zones, like secondary zones, obtain their records from other name servers. Their records are read only; therefore, administrators do not manually add, remove, or modify the records.
Stub zone records are also periodically refreshed, just like secondary zone records. However, secondary name servers contain a complete copy of the zone data on the primary server. Therefore, zone transfers from a primary server to a secondary server, or between secondary servers, can increase CPU usage and consume excessive bandwidth. A name server hosting a stub zone maintains a much smaller set of records; therefore, updates are less CPU intensive and consume less bandwidth.
When a name server hosting a stub zone receives a query for a domain name that it determines is in the stub zone, the name server uses the records in the stub zone to locate the correct name server to query, eliminating the need to query the root server.
Figure 19.8 and Figure 19.9 illustrate how the NIOS appliance resolves a query for a domain name for which it is not authoritative. Figure 19.8 illustrates how the appliance resolves a query when it does not have a stub zone.
Figure 19.9 illustrates how the appliance resolves the query with a stub zone.
In Figure 19.8, a client sends a query for ftp.sales.corp200.com to the NIOS appliance. When the appliance receives the request from the client, it checks if it has the data to resolve the query. If the appliance does not have the data, it tries to locate the authoritative name server for the requested domain name. It sends nonrecursive queries to a root name server and to the closest known name servers until it learns the correct authoritative name server to query.
Figure 19.8 Processing a Query without a Stub Zone...
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In Figure 19.9, when the NIOS appliance receives the request for the domain name in corp200.com, it determines it does not have the resource records to resolve the query. It does, however, have a list of the authoritative name servers in the stub zone, corp200.com. The appliance then sends a query directly to the name server in corp200.com.
Figure 19.9 Processing a Query with a Stub Zone...
