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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 5 Managing Switch Stacks Understanding Switch Stacks
As described in the hardware installation guide, you can use the Master LED on the switch to see if the
switch is the stack master.
Switch Stack Bridge ID and Router MAC Address
The bridge ID and router MAC address identify the switch stack in the network. When the switch stack
initializes, the MAC address of the stack master determines the bridge ID and router MAC address.
If the stack master changes, the MAC address of the new stack master determines the new bridge ID and
router MAC address. However, when the persistent MAC address feature is enabled, the stack MAC
address changes in approximately 4 minutes. During this time period, if the previous stack master rejoins
the stack, the stack continues to use its MAC address as the stack MAC address, even if the switch is
now a stack member and not a stack master. If the previous stack master does not rejoin the stack during
this period, the switch stack takes the MAC address of the new stack master as the stack MAC address.
See Enabling Persistent MAC Address, page 5-20 for more information.
Stack Member Numbers
The stack member number (1 to 9) identifies each member in the switch stack. The member number also
determines the interface-level configuration that a stack member uses. You can display the stack member
number by using the show switch user EXEC command.
A new, out-of-the-box switch (one that has not joined a switch stack or has not been manually assigned
a stack member number) ships with a default stack member number of 1. When it joins a switch stack,
its default stack member number changes to the lowest available member number in the stack.
Stack members in the same switch stack cannot have the same stack member number. Every stack
member, including a standalone switch, retains its member number until you manually change the
number or unless the number is already being used by another member in the stack.
• If you manually change the stack member number by using the switch
current-stack-member-number renumber new-stack-member-number global configuration
command, the new number goes into effect after that stack member resets (or after you use the
reload slot stack-member-number privileged EXEC command) and only if that number is not
already assigned to any other members in the stack. For more information, see the “Assigning a
Stack Member Number” section on page 5-22. Another way to change the stack member number is
by changing the SWITCH_NUMBER environment variable, as explained in the “Controlling
Environment Variables” section on page 3-20.
If the number is being used by another member in the stack, the switch selects the lowest available
number in the stack.
If you manually change the number of a stack member and no interface-level configuration is
associated with that new member number, that stack member resets to its default configuration. For
more information about stack member numbers and configurations, see the “Switch Stack
Configuration Files” section on page 5-15.
You cannot use the switch current-stack-member-number renumber new-stack-member-number
global configuration command on a provisioned switch. If you do, the command is rejected.
• If you move a stack member to a different switch stack, the stack member retains its number only if
the number is not being used by another member in the stack. If it is being used, the switch selects
the lowest available number in the stack.