When your stack is operational, one switch is the primary switch, responsible for running network protocols and managing the stack.
To provide recovery in case of a break in the stack connections, you can configure redundancy by designating a backup switch to take over as primary if the primary switch fails. When you perform the initial software configuration of the stack, the “easy setup” configuration option automatically configures redundancy, with slot 1 as the primary and slot 2 as the backup. You can also configure additional switches as “primary-capable,” meaning they can become a stack primary in case the initial backup switch fails.
When assigning the primary and backup roles in mixed stacks, consider the feature scalability and the speed of each switch model. The easy setup configuration process selects primary and backup switches based on capability and speed. The following list shows the capabilities based on the ability to cross stack with other switch families. The most capable switches are shown at the top of each list:
5520 Series switches can be stacked with themselves, or with 5320 Series or 5420 Series switches using Alternate stacking.
Beginning with Switch Engine 31.5, 5520 Series switches can be stacked with the 5420 Series switches using SummitStack-V80 and a special cable which converts QSFP+ to SFP-DD. The SummitStack-V80 configuration sets the speed of the QSFP+ stack ports to 20Gb.
Beginning with Switch Engine 31.6, 5520 Series switches can stack with 5320 Series switches by installing a 5520-VIM-4X VIM. The last two ports on the 5520-VIM-4X can be used as 10 GbE stack ports when Alternate stacking is selected. The two stack ports on the 5520-VIM-4X support both SFP+ direct attach and optical transceivers.
5520 Series switches can be stacked with 5720 Series switches using Native V200 stacking (SummitStack-V200). Primary and backup roles must be assigned to switches from the same series. For example, if the primary node is a 5520 Series switch, the backup node must also be a 5520 Series switch. The 5720 Series switches must only be used as standby nodes when they are in a mixed stack with 5520 Series switches. Similarly, if the primary node is a 5720 Series switch, the backup node must also be a 5720 Series switch.
When easy setup compares two switches that have the same capability, the lower slot number takes precedence.
Follow the same ranking hierarchy when you plan the physical placement of the switches in the stack.