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7 Planning and Creating a Switch Stack (Only the Cisco
Catalyst Blade Switch 3120 for HP)
A switch stack is a set of up to nine stacking-capable switch modules that are connected through their
StackWise Plus ports. One of the switches controls the operation of the stack and is called the stack
master. The stack master and the other switches in the stack are stack members. Layer 2 and Layer 3
protocols present the entire switch stack as a single entity to the network. Stacking is optional.
Caution The Cisco Catalyst Blade Switch 3120 for HP switch modules do not support switch
stacks with other types of blades switches as members. Combining the Cisco Catalyst
Blade Switch 3120 for HP with other types of blade switches in a switch stack might cause
the switch to work improperly or to fail.
When switch modules are not stacked, each acts as a standalone switch. For general concepts and
procedures to manage switch stacks, see the switch module software configuration guide and
command reference.
Before you connect the switch modules in a stack, keep in mind these stacking guidelines:
•You should install the stack master switch module and run the initial setup program on that switch
module before you connect the StackWise Plus cables to other stack members. We recommend that
you assign the highest priority value to the switch module that you prefer to be the stack master.
This ensures that the switch is re-elected as stack master if a re-election occurs. As you add new
switch modules to the stack, they automatically become stack members.
To assign a priority value through the Onboard Administrator after you have installed and initially
configured the first switch module, see the “Setting the Installed Switch to be the Stack Master
(Only Cisco Catalyst Blade Switch 3120 for HP Switches)” section on page 18.
•When you connect the StackWise Plus cables and create a stack, you can communicate with the
master switch internal Ethernet management port (Fa0) port, but not with the Fa0 ports of the
member switches. Only one Fa0 interface can be active, and that interface is the one on the active
stack master.
•For conditions that might cause a stack master re-election or to manually elect the stack master,
see the “Managing Switch Stacks” chapter in the switch module software configuration guide.
•You can stack any combination of up to nine Catalyst 3120G and 3120X switches. You can stack
only the Cisco Catalyst Blade Switch 3120 for HP switch modules; other switches are not
supported.
•Before installation, check the StackWise Plus cable length. Depending on your configuration, you
might need different sized cables. If you do not specify the length of the StackWise Plus cable when
you order your product, the 1-meter cable is supplied. If you need the 0.5-meter cable or the
3-meter cable, you can order these StackWise Plus cables from your Cisco sales representative: