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
•Operation
•Traffic Flow
Features
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
|
|
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 |
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 |
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.
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.
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 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.