3Com SUPERSTACK 3 WEBCACHE 3000, User Manual

Page: 54 / 362

54 C
HAPTER
1: W
EB
C
ACHING
C
ONCEPTS AND
D
EPLOYMENT
You can configure a child Webcache to forward requests to up to four
parent Webcaches. If one of the parent Webcaches does not have the
requested content or is unavailable, the child Webcache will
automatically try the next specified parent Webcache. If none of the
parent Webcaches are available, the child Webcache will forward its
request to the origin server.
If you do not want all cache misses to be forwarded to the parent
Webaches, you can configure an Exclusion List on the child Webcache.
You can specify IP addresses, IP address ranges and domain names that
the child Webcache should request directly from the origin server instead
of from the parent Webcaches.
Example
You may want to exclude cache misses to a LAN server in your network. If
you choose not to exclude the server, the cache misses will be forwarded
across the network to the parent Webcaches and then back again, rather
than being retrieved directly from the local server.
All client machines and Web sites that you specify in the Cache Bypass
screen will not be sent to the parent Webcaches; for further information,
see
“Cache Bypass” on page 186 .
How does Parent
Caching Work?
Parent Caching operates in the following way:
1 A URL is entered into a Web browser by a user on a client machine in
your network.
2 The child Webcache receives the request for the URL from the client
machine and checks its cache for the requested content.
3 If the content is not in the cache or the content is expired (see “Current
and Expired Content” on page 32 ), the child Webcache forwards the
request to the parent Webcache.
4 If the content is in the parent Webcache it is simultaneously served to the
client machine and stored in the child Webcache, as shown in
Figure 14 .
Subsequent requests for that content will be served directly from the child
Webcache.
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