Catalyst 6500 Series Switch Content Switching Module Installation and Configuration Note, 3.2
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Product Overview

Table Of Contents

Product Overview


Front Panel Description

Status LED

RJ-45 Connector


Traffic Flow

Product Overview

The Catalyst 6500 series Content Switching Module (CSM) provides high-performance server load balancing (SLB) among groups of servers, server farms, firewalls, caches, VPN termination devices, and other network devices, based on Layer 3 as well as Layer 4 through Layer 7 packet information.

Server farms are groups of load-balanced devices. Server farms that are represented as virtual servers can improve scalability and availability of services for your network. You can add new servers and remove failed or existing servers at any time without affecting the virtual server's availability.

Clients connect to the CSM directing their requests to the virtual IP (VIP) address of the virtual server. When a client initiates a connection to the virtual server, the CSM chooses a real server (a physical device that is assigned to a server farm) for the connection based on configured load-balancing algorithms and policies (access rules). Policies manage traffic by defining where to send client connections.

Sticky connections limit traffic to individual servers by allowing multiple connections from the same client to stick (or attach) to the same real server using source IP addresses, source IP subnets, cookies, and the secure socket layer (SSL) or by redirecting these connections using Hypertext Transfer Protocol (HTTP) redirect messages.

These sections describe the CSM:


Front Panel Description


Traffic Flow


Table 1-1 lists the new CSM features in this release.

Table 1-1 New CSM Feature Set Description 

Features New in this Release

Added management features from release 3.1(1)

Includes the XML DTD (document definition type), the Cisco IOS MIB extensions for the CSM, and the system object identifier (SYSOB ID MIB).

Backup (sorry server)

Allows a backup at the real server level.

Denial of service (DoS) improvements

Allows TCP termination for all connections to the CSM providing SYN attacks.

Failover improvements

Provides enhancements for preempt delay, the forced failover command, Layer 2 MAC address rewrites, and improved tracking.

Idle and pending timeouts

Allows for the configuration of the idle and pending timeouts for server-initiated connections.

Improved TCL (Toolkit Command Language) functionality

Provides User Datagram Protocol (UDP) socket and global variable support.

Increased VLAN support

Supports up to 512 server and client VLANs.

Jumbo Frame support

Jumbo Frame support has been added to the CSM software release 3.2 to allow support of frames of up to 9 KB for Layer 4 load balancing.

Limited MIB write support

Allow you to change the weights of servers.

Load balancing per packet

Allows the CSM to make load balancing decisions without creating a flow. This feature is useful when load balancing UDP traffic with flows that exist for a short time period, such as DNS.

Route lookup

Allows the CSM to work more efficiently with upstream gateways regardless of their redundancy implementation (HSRP, VRRP, proprietary, etc.)

Stateful Firewall Load Balancing (FWLB)

Allows all connections, both existing and new, to failover to the secondary firewall in a redundant pair. This feature works only with active-active stateful firewall configurations.

Static ARP entry

Provides the ability to manually add entries to the CSM ARP table.

Static sticky entries

The sticky table can be prepopulated with entries to force certain users to connect to specific servers.

Sticky debug tools

Includes a show command for the number of sticky table entries and the ability to enter a specific IP address and receive the sticky information for that IP address.

TCP fragments

Provides support for fragmented TCP packets.

UDP Probe

Provides the ability to send UDP probes to specified ports to verify that the CSM does not receive a "port unreachable" message.

XML configuration from TCL scripts

Adds the ability to send CSM configuration commands within a TCL script.

Table 1-2 lists the CSM features available in this release and previous releases.

Table 1-2 CSM Feature Set Description 

Supported Hardware

Supervisor 1A with MSFC and PFC

Supervisor 2 with MSFC and PFC

Supervisor 720—requires CSM software release 3.1(4) or later

Supported Protocols

TCP load balancing

UDP generic IP protocol load balancing

Special application-layer support for FTP and the Real Time Streaming Protocol (RTSP)

Layer 7 Functionality

Full regular expression matching

URL, cookie switching, Generic HTTP header parsing, HTTP method parsing

Miscellaneous Functionality

VIP connection watermarks

Backup (sorry server) and server farm

Optional port for health probes

IP reassembly

TCL (Toolkit Command Language) scripting

XML configuration interface


GSLB (Global Server Load Balancing)-requires a license

Resource usage display

Configurable idle and pending connection timeout

Idle timeout for unidirectional flows

STE integration for SSL load balancing

Real server names

TCP connection redundancy for all types of flows (TCP, UDP, and IP)

Fault tolerant show command enhancements

IOS SLB FWLB interoperation (IP reverse-sticky)

Multiple CSMs in a chassis

CSM and IOS-SLB functioning simultaneously in a chassis

Configurable HTTP 1.1 persistence (either all GETs are made to the same server or are balanced to multiple servers)

Fully configurable NAT

Server-initiated connections

Route health injection

Load-balancing Algorithms


Weighted round-robin (WRR)

Least connections

Weighted least connections

URL hashing

Source IP hashing (configurable mask)

Destination IP hashing (configurable mask)

Source and Destination IP hashing (configurable mask)

Load Balancing Supported

Server load balancing (TCP, UDP, or generic IP protocols)

Firewall load balancing

DNS load balancing

Stealth firewall load balancing

Transparent cache redirection

Reverse proxy cache

SSL off-loading

VPN-Ipsec load balancing

Generic IP devices and protocols


Cookie sticky with configurable offset and length


Source IP (configurable mask)

HTTP redirection


Sticky state

Full stateful failover (connection redundancy)

Health Checking








Return error-code checking

Inband health checking

User-defined TCL scripts


SNMP traps

Full SNMP and MIB support

XML interface for remote CSM configuration

Front Panel Description

Figure 1-1 shows the CSM front panel.

Figure 1-1 Content Switching Module Front Panel

Note The RJ-45 connector is covered by a removable plate.

Status LED

When the CSM powers up, it initializes various hardware components and communicates with the supervisor engine. The Status LED indicates the supervisor engine operations and the initialization results. During the normal initialization sequence, the status LED changes from off to red, orange, and green.

Note For more information on the supervisor engine LEDs, refer to the Catalyst 6500 Series Switch Module Installation Guide.

Table 1-3 describes the Status LED operation.

Table 1-3 Content Switching Module Status LED 



The module is waiting for the supervisor engine to provide power.

The module is not online.

The module is not receiving power, which could be caused by the following:

Power is not available to the CSM.

Module temperature is over the limit1 .


The module is released from reset by the supervisor engine and is booting.

If the boot code fails to run, the LED stays red after power up.


The module is initializing hardware or communicating with the supervisor engine.

A fault occurred during the initialization sequence.

The module has failed to download its Field Programmable Gate Arrays (FPGAs) on power up but continues with the remainder of the initialization sequence and provides the module online status from the supervisor engine.

The module has not received module online status from the supervisor engine. This problem could be caused by the supervisor engine detecting a failure in an external loopback test that it issued to the CSM.


The module is operational; the supervisor engine has provided module online status.

Green to orange

The module is disabled through the supervisor engine CLI 2 using the set module disable mod command.

1 Enter the show environment temperature mod command to display the temperature of each of four sensors on the CSM.

2 CLI = command-line interface.

RJ-45 Connector

The RJ-45 connector, which is covered by a removable plate, is used to connect a management station device or a test device. This connector is used by field engineers to perform testing and to obtain dump information.


Clients and servers communicate through the CSM using Layer 2 and Layer 3 technology in a specific VLAN configuration. (See Figure 1-2.) In a simple Server Load Balancing (SLB) deployment, clients connect to the client-side VLAN and servers connect to the server-side VLAN. Servers and clients can exist on different subnets. Servers can also be located one or more Layer 3 hops away and connect to the CSM through routers.

A client sends a request to one of the module's VIP addresses. The CSM forwards this request to a server that can respond to the request. The server then forwards the response to the CSM, and the CSM forwards the response to the client.

When the client-side and server-side VLANs are on the same subnets, you can configure the CSM in single subnet (bridge) mode. For more information, see the "Configuring the Single Subnet (Bridge) Mode" section.

When the client-side and server-side VLANs are on different subnets, you can configure the CSM to operate in a secure (router) mode. For more information, see the "Configuring the Secure (Router) Mode" section.

You can set up a fault-tolerant configuration in either the secure (router) or single subnet (bridged) mode using redundant CSMs. For more information, see the "Configuring Fault Tolerance" section.

Single subnet (bridge) mode and secure (router) mode can coexist in the same CSM with multiple VLANs.

Figure 1-2 Content Switching Module and Servers

Traffic Flow

This section describes how the traffic flows between the client and server in a CSM environment. (See Figure 1-3.)

Figure 1-3 Traffic Flow Between Client and Server

Note The numbers in Figure 1-3 correspond to the steps in the following procedure.

When you enter a request for information by entering a URL, the traffic flows as follows:

1. You enter a URL. (Figure 1-3 shows as an example.)

2. The client contacts a DNS server to locate the IP address associated with the URL.

3. The DNS server sends the IP address of the virtual IP (VIP) to the client.

4. The client uses the IP address (CSM VIP) to send the HTTP request to the CSM.

5. The CSM receives the request with the URL, makes a load-balancing decision, and selects a server.

For example, in Figure 1-3, the CSM selects a server (X server) from the server pool, replacing its own VIP address with the address of the X server (directed mode), and forwards the traffic to the X server. If the NAT server option is disabled, the VIP address remains unchanged (dispatch mode).

6. The CSM performs Network Address Translation (NAT) and eventually TCP sequence numbers translation.