Stacking Configuration Guidelines

Before you configure a stack, consider the following guidelines:

  • Plan the number of units and how the stacking ports on the units will be connected. For more information, refer to the hardware installation guide for your device.
  • The stack should be physically cabled in a linear or ring topology. Connect only those units that will be active in the stack.
  • Make sure all units intended for the stack are running the same software version. On any of the console ports in the stack, use the show version command to view all units, or the show version unit unit-number command to view an individual unit.
Note: If you are running a router image and there is a potential loop in your topology, you must configure the Spanning Tree Protocol in the would-be active controller. Otherwise, excessive looping packets may affect stack formation. The Spanning Tree Protocol is enabled by default in switch images.

Note: If STP is not enabled, there may be a loop issue when multiple cables are used to connect a standalone unit to a stack. The loop does not affect stack formation. The loop issue disappears after the multiple links are converted to stacking trunks when the standalone unit is integrated to the stack. However, temporary looping may cause some data traffic interruption.

Note: If you want to enlarge a live link or change a linear stack to a ring in a production network, it is better to use stack-port or stack-trunk commands or, for live links, multi-stack-trunk commands to make the configuration changes before you connect the new links. If you connect new links first without the new configuration, the new links cause Layer 2 loops and possible data traffic interruption. After you run stack interactive-setup to discover these new links and generate new configuration for the new links, the loop issue disappears.

  • When you have a stack of eight or more units, you may need to increase the trap hold time from the default (60 seconds) to five minutes (300 seconds). This will prevent the loss of initial boot traps. To increase the trap hold time, use the following command. 
device# configure terminal
device(config)# snmp-server enable traps holddown-time 300
Parent topic: Planning to Build a Stack