Cisco Systems 3750E manual Wccp and Switch Stacks, 41-4

Chapter 41 Configuring Web 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 clients 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 web 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 web 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 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.

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.

WCCP and Switch Stacks

WCCP support is the same for a switch stack as for a standalone switch. WCCP configuration information is propagated to all switches in the stack. All switches in the stack, including the stack master, process the information and program their hardware. For more information about switch stacks, see Chapter 5, “Managing Switch Stacks.”

The stack master performs these WCCP functions:

•It receives protocol packets from any WCCP-enabled interface and sends them out any WCCP-enabled interface in the stack.

•It processes the WCCP configuration and propagates the information to all stack members.

•It distributes the WCCP information to any switch that joins the stack.

•It programs its hardware with the WCCP information it processes.

Stack members receive the WCCP information from the master switch and program their hardware.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

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