Chapter 7 Web cache configuration 203Using the BayStack Instant Internet Management Software Version 7.11Before the Instant Internet unit sends requested Web content to the user, itevaluates each Web entry and then does one of two things:• If the entry is not already in the cache, the cache server retrieves the entryfrom the originating Web server, caches it, and then sends the entry to theuser.• If the entry is in the cache, the cache server evaluates the date and time of theentry and then does one of the following:— If the entry in the cache is still fresh, the cache server sends the entry inthe cache to the user.— If the entry in the cache is expired, the cache server sends a conditionalrequest to the originating Web server. If the data on the server haschanged, it replaces the cached entry with the new entry from theoriginating Web server, and then sends the new entry to the user.How Web caching works with a user’s local cacheAs a downstream caching proxy server, the Instant Internet unit is located betweena user’s workstation on the network and the Internet. If you disable the local cacheon a user’s Web browser, the Instant Internet unit is the user’s primary cache andall requests for Web content go directly to the cache server. If you enable the localcache, the cache server is a secondary cache. Requests for Web content aredirected first to the user’s local cache, and then to the Instant Internet unit.Although using the Instant Internet unit as the only cache slightly increases trafficon your local network, doing so provides several advantages. This setup:• Frees up hard disk space on each user’s workstation by eliminating the need toreserve space for caching.• Increases the number of entries in the cache that are available to all users.• Increases cache statistics because all requests for Web content pass throughthe Instant Internet unit which gives the truest measure of the efficiency of thecache.
