45-4
Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter45 Configuring Cache Services By Using WCCP
Understanding WCCP
You can configure up to 8 service groups on a switch or switch stack and up to 32 cache engines per
service group. WCCP maintains the priority of the service group in the group definition. WCCP uses the
priority to configure the service groups in the switch hardware. For example, if service group 1 has a
priority of 100 and looks for destination port 80, and service group 2 has a priority of 50 and looks for
source port 80, the incoming packet with source and destination port 80 is forwarded by using service
group 1 because it has the higher priority.
WCCP supports a cluster of application engines for every service group. Redirected traffic can be sent
to any one of the application engines. The switch supports the mask assignment method of load
balancing the traffic among the application engines in the cluster for a service group.
After WCCP is configured on the switch, the switch forwards all service group packets received from
clients to the application engines. However, these packets are not redirected:
•Packets originating from the application engine and targeted to the server.
•Packets originating from the application engine and targeted to the client.
•Packets returned or rejected by the application engine. These packets are sent to the server.
You can configure a single multicast address per service group for sending and receiving protocol
messages. When there is a single multicast address, the application engine sends a notification to one
address, which provides coverage for all routers in the service group, for example, 225.0.0.0. If you add
and remove routers dynamically, using a single multicast address provides easier configuration because
you do not need to specifically enter the addresses of all devices in the WCCP network.
You can use a router group list to validate the protocol packets received from the application engine.
Packets matching the address in the group list are processed, packets not matching the group list address
are dropped.
To disable caching for specific clients, servers, or client/server pairs, you can use a WCCP redirect
access control list (ACL). Packets that do not match the redirect ACL bypass the cache and are forwarded
normally.
Before WCCP packets are redirected, the switch examines ACLs associated with all inbound features
configured on the interface and permits or denies packet forwarding based on how the packet matches
the entries in the ACL.
Note Only permit ACL entries are supported in WCCP redirect lists.
When packets are redirected, the output ACLs associated with the redirected interface are applied to the
packets. Any ACLs associated with the original port are not applied unless you specifically configure
the required output ACLs on the redirected interfaces.