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| User |-------------->| |---------|->|Foreign | <BR> | Program | | Resolver | | | Name | <BR> | |<--------------| |<--------|--| Server | <BR> | | user responses| |responses| | | <BR> +---------+ +----------+ | +--------+ <BR> | A | <BR> cache additions | | references | <BR> V | | <BR> +----------+ | <BR> | Shared | | <BR> | database | | <BR> +----------+ | <BR> A | | <BR> +---------+ refreshes | | references | <BR> / /| | V | <BR> +---------+ | +----------+ | +--------+ <BR> | | | | |responses| | | <BR> | | | | Name |---------|->|Foreign | <BR> | Master |-------------->| Server | | |Resolver| <BR> | files | | | |<--------|--| | <BR> | |/ | | queries | +--------+ <BR> +---------+ +----------+ | <BR> A |maintenance | +--------+ <BR> | +------------|->| | <BR> | queries | |Foreign | <BR> | | | Name | <BR> +------------------|--| Server | <BR> maintenance responses | +--------+ <BR> <BR>The shared database holds domain space data for the local name server <BR>and resolver. The contents of the shared database will typically be a <BR>mixture of authoritative data maintained by the periodic refresh <BR>operations of the name server and cached data from previous resolver <BR>requests. The structure of the domain data and the necessity for <BR>synchronization between name servers and resolvers imply the general <BR>characteristics of this database, but the actual format is up to the <BR>local implementor. <BR> <BR> <BR> <BR> <BR>Mockapetris [Page 6] <BR> <BR>RFC 1035 Domain Implementation and Specification November 1987 <BR> <BR> <BR>Information flow can also be tailored so that a group of hosts act <BR>together to optimize activities. Sometimes this is done to offload less <BR>capable hosts so that they do not have to implement a full resolver. <BR>This can be appropriate for PCs or hosts which want to minimize the <BR>amount of new network code which is required. This scheme can also <BR>allow a group of hosts can share a small number of caches rather than <BR>maintaining a large number of separate caches, on the premise that the <BR>centralized caches will have a higher hit ratio. In either case, <BR>resolvers are replaced with stub resolvers which act as front ends to <BR>resolvers located in a recursive server in one or more name servers <BR>known to perform that service: <BR> <BR> Local Hosts | Foreign <BR> | <BR> +---------+ | <BR> | | responses | <BR> | Stub |<--------------------+ | <BR> | Resolver| | | <BR> | |----------------+ | | <BR> +---------+ recursive | | | <BR> queries | | | <BR> V | | <BR> +---------+ recursive +----------+ | +--------+ <BR> | | queries | |queries | | | <BR> | Stub |-------------->| Recursive|---------|->|Foreign | <BR> | Resolver| | Server | | | Name | <BR> | |<--------------| |<--------|--| Server | <BR> +---------+ responses | |responses| | | <BR>
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