Catalyst 4500 Series Switch Software Configuration Guide, 15.0(2)SG Configuration Guide

Overview

WCCP is a Cisco-developed content-routing technology that enables you to integrate content engines into your network infrastructure.

The Cisco IOS WCCP feature allows use of Cisco Content Engines (or other content engines running WCCP) to localize web traffic patterns in the network, enabling content requests to be fulfilled locally. Traffic localization reduces transmission costs and download time.

WCCP enables Cisco IOS routing platforms to transparently redirect content requests. The main benefit of transparent redirection of HTTP/non-http requests is that users need not configure their browsers to use a web proxy. Instead, they can use the target URL to request content, and have their requests automatically redirected to a content engine. The word “transparent” is this case means that the end user does not know that a requested file (such as a web page) came from the content engine instead of from the originally specified server.

When a content engine receives a request, it attempts to service it from its own local content. If the requested information is not present, the content engine issues its own request to the originally targeted server to get the required information. When the content engine retrieves the requested information, it forwards it to the requesting client and caches it to fulfill future requests, thus maximizing download performance and substantially reducing transmission costs.

WCCP enables a series of content engines, called a content engine cluster, to provide content to a router or multiple routers. Network administrators can easily scale their content engines to handle heavy traffic loads using these clustering capabilities. Cisco clustering technology enables each content member to work in parallel, resulting in linear scalability. Clustering content engines greatly improves the scalability, redundancy, and availability of your caching solution. You can cluster up to 32 content engines to scale to your desired capacity.

Hardware Acceleration

Hardware Acceleration is enabled by default on Catalyst 4500 series switches. Layer 2 rewrite forwarding and Layer 2 return method are supported in hardware; GRE return method is supported in software.

You must configure a directly connected Content Engine to negotiate use of the WCCP Layer 2 Redirection feature with load balancing based on the mask assignment table. The show ip wccp web-cache detail command displays the redirection method for each cache.

Note You can configure Cisco Content Engine Release 2.2 or later to use the WCCP Layer 2 redirection feature with the mask assignment table.

Understanding WCCP Configuration

Multiple routers can use WCCP to service a cache cluster. Figure 1-1 illustrates a sample configuration using multiple routers.

Figure 1-1 Cisco Content Engine Network Configuration Using WCCP

The subset of content engines within a cluster and routers connected to the cluster that are running the same service is known as a service group. Available services include TCP and User Datagram Protocol (UDP) redirection.

WCCP requires that each content engine be aware of all the routers in the service group. To specify the addresses of all the routers in a service group, you must choose one of the following methods:

• Unicast—A list of IP addresses for each of the routers in the group is configured on each content engine. In this case the address of each router in the group must be explicitly specified for each content engine during configuration.
• Multicast—A single multicast address is configured on each content engine. In the multicast address method, the content engine sends a single-address notification that provides coverage for all routers in the service group. For example, a content engine could indicate that packets should be sent to a multicast address of 224.0.0.100, which would send a multicast packet to all routers in the service group configured for group listening using WCCP (see the ip wccp group-listen interface configuration command for details).

The multicast option is easier to configure because you need only specify a single IP address on each content engine. This option also enables you to add and remove routers from a service group dynamically without needing to reconfigure the content engines with a different list of addresses each time.

The following sequence of events describe how WCCP works:

1. Each WCCP client (content engine) is configured with a list of WCCP servers (routers).

2. Each content engine announces its presence with a "Here I Am" message and a list of routers with which it has established communication. Similarly, the routers reply with their view (list) of content engines in the service group through "I See You" messages.

3. Once the view is consistent across all content engines in the cluster, one content engine is designated as the lead and sets the policy that the switches need to deploy in redirecting traffic.

WCCP Features

These sections describe WCCP features:

• HTTP and Non-HTTP Services Support
• Multiple Routers Support
• MD5 Security
• Web Content Packet Return

HTTP and Non-HTTP Services Support

WCCP enables redirection of HTTP traffic (TCP port 80 traffic), as well as non-HTTP traffic (TCP and UDP). WCCP supports the redirection of packets intended for other ports, including those used for proxy-web cache handling, File Transfer Protocol (FTP) caching, FTP proxy handling, web caching for ports other than 80, and real audio, video, and telephony applications.

To accommodate the various types of services available, WCCP introduces the concept of multiple service groups. Service information is specified in the WCCP configuration commands using dynamic services identification numbers (such as “98”) or a predefined service keywords (such as “web-cache”). This information is used to validate that service group members are all using or providing the same service.

Note The Catalyst 4500 series switch supports up to eight service groups.

For information on supported WCCP version 2 services with ACNS version 5.2 software, refer to the
Release Notes for Cisco ACNS Software, Release 5.2.3.

The content engines in service group specify traffic to be redirected by protocol (TCP or UDP) and port (source or destination). Each service group has a priority level assigned to it. Packets are matched against service groups in priority order and redirected by the highest priority service group that matches traffic characteristics.

Multiple Routers Support

WCCP enables you to attach multiple routers to a cluster of cache engines. The use of multiple routers in a service group enables redundancy, interface aggregation, and distribution of the redirection load.

MD5 Security

WCCP provides optional authentication that enables you to control which routers and content engines become part of the service group using passwords and the HMAC MD5 standard. Shared-secret MD5 one-time authentication (set using the ip wccp [ password [ 0-7 ] password ] global configuration command) enables messages to be protected against interception, inspection, and replay.

Web Content Packet Return

If a content engine is unable to provide a requested object it has cached due to error or overload, the content engine returns the request to the router for onward transmission to the originally specified destination server. WCCP verifies which requests have been returned from the content engine unserviced. Using this information, the router can then forward the request to the originally targeted server (rather than attempting to resend the request to the content cluster). This provides error handling transparency to clients.

Typical reasons why a content engine would reject packets and initiate the packet return feature include the following:

• Instances when the content engine is overloaded and has no room to service the packets.
• Instances when the content engine is filtering for certain conditions that make caching packets counterproductive (such as, when IP authentication has been turned on).

Configuring a Service Group Using WCCP

WCCP uses service groups based on logical redirection services. The standard service is the content engine, which intercepts TCP port 80 (HTTP) traffic and redirects that traffic to the content engines. This service is referred to as a well-known service, because the characteristics of the web cache service are known by both the router and content engines. A description of a well-known service is not required beyond a service identification (the command line interface (CLI) provides a web-cache keyword in the command syntax).

For information on supported WCCP services with ACNS version 5.2 software, refer to the
Release Notes for Cisco ACNS Software, Release 5.2.3.

In addition to the web cache service, there can be up to seven dynamic services running concurrently on the switch.

Note More than one service can run on a switch at the same time, and routers and content engines can be part of multiple service groups at the same time.

The dynamic services are defined by the content engines; the content engine instructs the router which protocol or ports to intercept, and how to distribute the traffic. The router itself does not have information on the characteristics of the dynamic service group’s traffic, because this information is provided by the first content engine to join the group. In a dynamic service, up to eight ports can be specified within a single protocol TCP or UDP).

Cisco Content Engines, for example, use dynamic service 99 to specify a reverse-proxy service. However, other content engines may use this service number for some other service. The following configuration information deals with enabling general services on Cisco routers. Refer to the content engine documentation for information on configuring services on content engines.

To enable a service on a Catalyst 4500 series switch, perform this task:

Specifying a Web Cache Service

To configure a web-cache service and ingress redirection, perform this task:

To configure a web-cache service and egress redirection, perform this task:

Using Access Lists for a WCCP Service Group

A Catalyst 4500 series switch can use an access list to restrict the content engines that can join a service group.

To restrict a content engine, perform this task:

Setting a Password for a Router and Cache Engines

MD5 password security requires that each content engine and Catalyst 4500 series switch that wants to join a service group be configured with the service group password. The password can consist of up to seven characters. Each content engine or Catalyst 4500 series switch in the service group authenticates the security component in a received WCCP packet immediately after validating the WCCP message header. Packets failing authentication are discarded.

To configure an MD5 password for use by the Catalyst 4500 series switch in WCCP communications, perform this task:

Performing a General WCCP Configuration Example

The following example shows a general WCCP configuration session. VLAN 20 is for the client interface. VLAN 50 is for the content engine interface.

Running a Web Cache Service Example

The following example shows a web cache service configuration session with ingress redirection:

Running a Reverse Proxy Service Example

The following example assumes you a configuring a service group using Cisco Content Engines, which use dynamic service 99 to run a reverse proxy service. The following example illustrates how to configure egress redirection, where VLAN 40 reflects the server interface and VLAN 50 reflects the content engine interface:

Running TCP-Promiscuous Service Example

The following example shows how to configure TCP promiscuous service, where VLAN 40 represents the server interface and VLAN 50 represents the content engine interface:

Running Redirect Access-List Example

Redirect access-list allows you to control which traffic to be redirected. The following example shows how to redirect traffic only from subnet 10.1.1.0:

Using Access Lists Example

To achieve better security, you can use a standard access list to notify the Catalyst 4500 series switch to which IP addresses are valid addresses for a content engine attempting to register with the current switch. The following example shows a standard access list configuration session where the access list number is 10 for some sample hosts:

Setting a Password for a Switch and Content Engines Example

The following example shows a WCCP password configuration session where the password is alaska1:

Verifying WCCP Settings Example

To verify your configuration changes, use the more system:running-config EXEC command. The following example shows that the both the web cache service and dynamic service 99 are enabled on the Catalyst 4500 series switch:

WCCP unicast mode

WCCP multicast mode