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:
•Features
•Front Panel Description
•CSM Operation
•CSM Traffic Flow
Features
This software release contains feature sets supporting CSM functionality from previous releases. The tables in this section list these feature sets.
Table 1-1 lists the new CSM features in this release.
Table 1-1 New CSM Feature Set Description
Features New in this Release
|
|
Server Application State Protocol (SASP) |
Allows the CSM to receive traffic weight recommendations from Workload Managers (WMs), to register with WMs and enable WMs to suggest new load balancing group members to the CSM. |
Table 1-2 lists the CSM features available in this release and previous releases.
Table 1-2 CSM Feature Set Description
|
|
Supervisor 1A with MSFC and PFC |
Supervisor 2 with MSFC and PFC |
Supervisor 720—requires CSM software release 3.1(4) or later |
|
TCP load balancing |
UDP generic IP protocol load balancing |
Special application-layer support for FTP and the Real Time Streaming Protocol (RTSP) |
|
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 |
SNMP |
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
|
Round-robin |
Weighted round-robin (WRR) |
Least connections with slow-start enable for real servers. |
Weighted least connections |
URL hashing |
Source IP hashing (configurable mask) |
Destination IP hashing (configurable mask) |
Source and destination IP hashing (configurable mask) |
|
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 |
SSL ID |
Source IP (configurable mask) |
HTTP redirection |
|
Sticky state |
Full stateful failover (connection redundancy) |
|
HTTP |
ICMP |
Telnet |
TCP |
FTP |
SMTP |
DNS |
Return error-code checking |
Inband health checking |
User-defined TCL scripts |
|
SNMP traps |
Full SNMP and MIB support |
XML interface for remote CSM configuration |
Back-end encryption support. |
Workgroup Manager Support
|
Server Application State Protocol (SASP) |
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
|
|
Off |
•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 . |
Red |
•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. |
Orange |
•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. |
Green |
•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. |
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.
CSM Operation
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 on page 2-1.
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 on page 2-4.
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 on page 7-1.
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
CSM 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 www.example.com 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 www.example.com 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.