How Webcache Support Works - 3Com 3C17205-US - Corp SUPERSTACK 3 SWITCH 4400 24PORT Implementation Manual

94 C 9: U
HAPTER SING
How Webcache
Support Works
W S
EBCACHE UPPORT
latency is reduced as the Webcache is able to deliver web content
faster than the time required to retrieve information over a WAN
connection.
Because the redirection decision is based upon the destination TCP port,
the solution is transparent to end users and requires no manual
configuration of web clients.
When a Webcache is added to your network the lowest numbered
Switch unit in a stack is elected as the master unit. The master unit
searches its internal database to retrieve the following information about
the Webcache: its IP address and status (enabled or disabled), and the
TCP port on which to redirect traffic. The master unit distributes this
information to the other units in the stack which update their internal
databases accordingly.
The master unit designates a polling unit — this can be the master unit or
another unit in the stack. The polling unit must have an IP address that is
on the same subnetwork as the Webcache. If multiple units are
configured in this way, then the master unit will select the first unit that
responds to be the polling unit. The polling unit polls for the Webcache
using the Webcache health check URL (see
page 95 for more information). When the polling unit receives a response
from the Webcache it resolves the Webcache's IP address to a MAC
address and a port and passes it to other units in the stack.
The Switch then redirects all incoming HTTP traffic on TCP port 80 to the
Webcache. If the Webcache health check fails, for example because the
Webcache has failed or been powered down, caching will be disabled
and HTTP traffic will be directed over the WAN connection.
Changing the TCP Port Number
You can choose a different TCP port number to specify the traffic which is
to be redirected to a SuperStack 3 Webcache. Normally TCP packets
addressed to TCP port 80 are redirected, as this is the standard port used
for the HTTP protocol on the World Wide Web. Certain specialized
environments may be using a different TCP port for HTTP traffic, and so
require that a different port number be redirected. In this case both the
Webcache and the Switch must be configured to handle that port.
"Cache Health Checks" on