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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter41 Configuring Web Cache Services By Using WCCP
Understanding WCCP
WCCP enables supported Cisco routers and switches to transparently redirect content requests. With
transparent redirection, users do not have to configure their browsers to use a web proxy. Instead, they
can use the target URL to request content, and their requests are automatically redirected to an
application engine. The word transparent means that the end user does not know that a requested file
(such as a web page) came from the application engine instead of from the originally specified server.
When an application engine receives a request, it attempts to service it from its own local cache. If the
requested information is not present, the application engine sends a separate request to the end server to
retrieve the requested information. After receiving the requested information, the application engine
forwards it to the requesting client and also caches it to fulfill future requests.
With WCCP, the application-engine cluster (a series of application engines) can service multiple routers
or switches, as shown Figure 41-1.
Figure 41-1 Cisco Cache Engine and WCCP Network Configuration
WCCP Message Exchange
This sequence of events describes the WCCP message exchange:
1. The application engines send their IP addresses to the WCCP-enabled switch by using WCCP,
signaling their presence through a Here I am message. The switch and application engines
communicate to each other through a control channel based on UDP port 2048.
2. The WCCP-enabled switch uses the application engine IP information to create a cluster view (a list
of application engines in the cluster). This view is sent through an I see you message to each
application engine in the cluster, essentially making all the application engines aware of each other.
A stable view is established after the membership of the cluster remains the same for a certain
amount of time.
3. When a stable view is established, the application engine in the cluster with the lowest IP address
is elected as the designated application engine.
Cache 1 Cache 2 Cache 3
Web
clients
100BASE-T
Layer 3
switches
201294
Internet