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This chapter explains how the Catalyst Stack improves network performance and covers the following topics:
There are two ways of configuring Catalyst 3000 series switches, either as a single stand-alone switch or as a logical combination of up to eight switches. This logical combination of switches is called a Catalyst Stack.
Catalyst 3000 series switches forming a Stack is a unique concept. Catalyst 3000 series switches as a Stack are not just a connection of several units of switches. A Catalyst 3000 series Stack virtually combines to form a single unit.
A Catalyst Stack is configured in either of the following two ways:
When a Catalyst 3000 series switch first powers up, it runs through a set of self-diagnostics. Immediately after the diagnostics are completed, the Catalyst 3000 series runs through a Stack discovery mode. This discovery mode is used to sense if the switch is cabled to another Catalyst 3000 series. If during the discovery mode the Catalyst 3000 series switch is connected to another unit(s), the switches automatically combine to form a Stack. At the end of the discovery mode, if a Catalyst 3000 series is not connected to another unit, it operates as a stand-alone switch.
There are no special tools, extra software, or expensive equipment needed to form a Stack of Catalyst 3000 series switches. Two switches can be connected to form a Stack by using only a Stack Port cable and an interface card plugged into the back of each Catalyst 3000 series. This creates a direct connection between the two switches, which is referred to as a back-to-back Stack. By using an eight-port Catalyst Matrix interface, a Stack of up to eight Catalyst 3000 series switches can be created.
See Chapter 4, "Installation," for details on how to cable Catalyst Stack equipment together.
The following sections describe in detail how a Stack is connected and formed. The back-to-back Stack is explained first, followed by an explanation of a Stack with an Catalyst Stack Matrix.
The Stack discovery mode runs after power-on diagnostics. If, during this discovery mode, a Catalyst 3000 series switch senses that it is connected to another Catalyst 3000 series switch in a back-to-back configuration, the two units begin to form a Stack.
As soon as the Stack discovery mode is completed, each switch is assigned a box number that is saved to NVRAM. One switch becomes Box 1 and the other switch becomes Box 2. The box number for each switch is determined by several factors. The following table, Table 0-1, presents the results of different combinations of two Catalyst 3000 series switches forming a back-to-back Stack, as of the 2.2 software release:
| Switches | Switch B Box 1, running | Switch B Box 2, running | Switch B no Box number, not running | Switch B Box 1, not running | Switch B Box 2, not running |
|---|---|---|---|---|---|
| Switch A Box 1, running | See section "Provider of Inter-box Parameters" |
No conflict | Switch A remains Box 1, Switch B would become Box 2 | Switch A remains Box 1, Switch B would become Box 2 |
No conflict
|
| Switch A Box 2, running |
No conflict
| See section "Provider of Inter-box Parameters" | Switch A remains Box 1, Switch B would become Box 2 |
No conflict
| Switch A remains Box 1, Switch B would become Box 2 |
| Switch A no Box number, not running | Switch B remains Box 1, Switch A would become Box 2 | Switch B remains Box 1, Switch A would become Box 2 | See section "Provider of Inter-box Parameters" | Switch B remains Box 1, Switch A would become Box 2 | Switch B remains Box 1, Switch A would become Box 2 |
| Switch A Box 1, not running | Switch B remains Box 1, Switch A would become Box 2 |
No conflict
| Switch A remains Box 1, Switch B would become Box 2 | See section "Provider of Inter-box Parameters" |
No conflict
|
| Switch A Box 2, not running |
No conflict
| Switch B remains Box 1, Switch A would become Box 2 | Switch A remains Box 1, Switch B would become Box 2 |
No conflict
| See section "Provider of Inter-box Parameters" |
The Catalyst 3000 series switches must combine configuration information so that both boxes, as a Stack, use certain common parameters. This common information is called the Inter-box Parameters (see this chapter's section, "Inter-box Parameters," for a list of these parameters). One Catalyst 3000 series switch must become the source, or provider, of the Inter-box Parameters.
After a Stack has formed and sets up the Inter-box Parameters, the Stack operates the same way, whether it is in a back-to-back configuration, or in a multi-unit configuration using the Catalyst Matrix interface.
Using a Catalyst Matrix, a multi-unit Stack of up to eight Catalyst 3000 series switches can be created. The following sections describe how this multi-unit Stack is formed.
The Catalyst Matrix is an eight-port, switch-matrix interface that connects up to eight Catalyst 3000 series switches. The switch senses if it is connected to a Catalyst Matrix and also senses if there are other Catalyst 3000 series switches connected to that Catalyst Matrix. The connected switches along with the Catalyst Matrix combine logically to form a Stack.
Any combination of up to eight Catalyst 3000 series switches can be connected to or disconnected from the Catalyst Matrix while it, or any of the units, are powered-on or powered-off. A proprietary shielded cable, one meter in length, with 50-pin connectors, is used to connect the Catalyst Stack equipment together. The cable has cross-over wiring so either end can connect to the Catalyst Matrix, or to the Catalyst 3000 series switches. The cable is plugged directly into a Stack Port I/O connector on the back of the Catalyst Matrix. The other end is plugged into a Catalyst Stack Port module interface card that is installed into the rear expansion slot in the Catalyst 3000 series switch.
For a description of the features and physical specifications of the Catalyst Matrix, see Chapter 1, "Catalyst 3100 Theory of Operation and Specifications," and see Chapter 4, "Installation," for details on how to install and connect the Catalyst Matrix and the Catalyst 3100. In this chapter, the following sections describe how a Stack is initially formed using a Catalyst Matrix.
When Catalyst 3000 series switches first power up, they run through a set of self-diagnostics. Immediately after the diagnostics are completed, the switches run through a Stack discovery mode. During this Stack discovery mode, if two or more switches are connected to a Catalyst Matrix, the units will sense the connection and combine logically to create a Stack configuration.
As soon as the Stack discovery mode is completed, two things happen:
The following sections describe the Inter-box parameters its functions.
Before a Stack is formed, there are potential configuration differences between Catalyst 3000 series switches forming a Stack. In order for a Stack to operate as a single entity, the Inter-box parameters must be the same in all of the switches in a Stack.
If all the switches are preconfigured with the same information, the procedure for Stack forming is as described in previous sections (back-to-back, or multi-unit Stack, respectively).
If the parameters are different in any of switches trying to form a Stack, the following procedures would apply:
The following is a list of these shared Inter-box parameters. The parameters in this list are accessed through the console configuration menus. The console menus are described in Chapter 7, "Console Configuration."
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