User manual

Network Setup
116
A proxy-cache server implements Internet object caching. This is a way to store
requested Internet objects (i.e., data available via HTTP, FTP, and other protocols) on a
server closer to the user's network than on the remote site. Typically the proxy-cache
server eliminates the need to re-download Internet objects over the available Internet
connection when several users attempt to access the same web site simultaneously.
The web site’s contents are available in the cache (server memory or disk) and quickly
accessible over the LAN rather than the slower Internet link.
The SG unit’s web cache keeps objects cached in memory and on a LAN network share,
caches Internet name (DNS) lookups and implements negative caching of failed
requests.
Using the lightweight Internet Cache Protocol, multiple web caches can be arranged in a
hierarchy or mesh. This allows web cache peers to pull objects from each other’s
caches, further improving the performance of web access for an organisation with
multiple Internet gateway.
The SG unit’s web cache may also be configured to pass off web transation requests or
responses to a third-party ICAP server for processing, using its ICAP client. This is
typically used to integrate a third-party virus scanning, content filtering or complete CSM
solution, such as WebWasher (http://www.webwasher.com).
Enabling the web cache
Select Web cache under Network Setup. Check Enable to enable the web cache.
Selecting a cache size
Select the amount of memory (RAM) on the SG unit to be reserved for caching Internet
objects. The maximum amount of memory you can safely reserve depends on what
other services the SG unit has running, such as VPN or a DHCP server.
If you are using a Network Share or Local Storage (recommended, see below), it is
generally best to set this to 8 Megabytes.
Otherwise, start with a small cache (8 Megabytes or 16 Megabytes) and gradually
increase it until you find a safe upper limit where the SG unit can still operate reliably.
Storage
The web cache is capable of utilizing a storage device attached via the USB port, or a
network share to provide backing store for the cache. Using this greatly increases the
effectiveness of the cache.