Accepted Solutions
Switch Stacking and Power Stacking Guidelines
Before connecting the switches in a stack, keep in mind these stacking guidelines:
Size of the switch and any optional power-supply module. The 1100-W power-supply module is longer than the other modules. Stacking switches with the same power-supply modules together makes it easier to cable the switches.
- Length of cable. Depending on the configurations that you have, you might need different-sized cables. If you do not specify the length of the StackWise cable, the 0.5-meter cable is supplied. If you need the 1-meter cable or the 3-meter cable, you can order it from your Cisco supplier. For cable part numbers, see StackWise Ports. The Data Stack Cabling Configurations provides examples of recommended configurations.
- For rack-mounted switch stacks that are members of a StackPower stack as well as a data stack, see Planning a StackPower Stack.
- You can create data stacks with up to nine switches in a stack.
Data Stack Cabling Configurations
This is an example of a recommended configuration that uses the supplied 0.5-meter StackWise cable. In this example, the switches are stacked in a vertical rack or on a table. This configuration provides redundant connections. The configuration example uses the supplied 0.5-meter StackWise cable. The example shows the full-ring configuration that provides redundant connections.
This example shows a recommended configuration when the switches are mounted side-by-side. Use the 1-meter and the 3-meter StackWise cables to connect the switches. This configuration provides redundant connections.
Data Stack Bandwidth and Partitioning Examples
This section provides examples of data stack bandwidth and possible data stack partitioning. The figure shows a data stack of Catalyst 3850 switches that provides full bandwidth and redundant StackWise cable connections.
This figure shows an example of a stack of Catalyst 3850 switches with incomplete StackWise cabling connections. This stack provides only half bandwidth and does not have redundant connections.
The figures below show data stacks of Catalyst 3850 switches with failover conditions. In this figure, the StackWise cable is bad in link 2. Therefore, this stack provides only half bandwidth and does not have redundant connections.
In this figure, link 2 is bad. Therefore, this stack partitions into two stacks, and the top and bottom switches become the active switch in the stack. If the bottom switch is a member (not active or standby switch), it reloads.
Power-On Sequence for Switch Stacks
Consider these guidelines before you power on the switches in a stack:
The sequence in which the switches are first powered on might affect the switch that becomes the stack master.
- There are two ways to elect an active switch:
- If you want a particular switch to become the active switch, configure it with the highest priority. Among switches with same priority, the switch with the lowest MAC address becomes the active switch.
If you want a particular switch to become the active switch, power on that switch first. This switch remains the active switch until a reelection is required. After 2 minutes, power on the other switches in the stack. If you have no preference as to which switch becomes the active switch, power on all the switches in the stack within 1 minute. These switches participate in the active switch election. Switches powered on after 2 minutes do not participate in the election.
If changes are made to the stack without powering down the switches, the following results can occur:
If two operating partial ring stacks are connected together using a stack cable, a stack merge can take place. This situation reloads the whole stack (all switches in the stack).
- If some switches in the stack are completely separated from the stack, a stack split can occur.
- A stack split can occur on a full ring stack if:
- In a split stack, depending on where the active and standby switches are located, either two stacks might be formed (with the standby taking over as the new active switch in the newly formed stack) or all the members in the newly formed stack might reload.
 Note | These results depend on how the switches are connected. You can remove two or more switches from the stack without splitting the stack. |
For conditions that can cause a stack reelection or to manually elect the active switch, see the stacking software configuration guide on Cisco.com at this URL: http://www.cisco.com/go/cat3850_docs.
Planning a StackPower Stack
StackPower Stacking Guidelines
You can configure a StackPower stack for either power sharing or redundancy. In power-sharing mode, the power of all the power supplies in the stack is aggregated and distributed among the stack members.
In redundant mode, when the total power budget of the stack is calculated, the wattage of the largest power supply is not included. That power is held in reserve and used to maintain power to switches and attached devices when one power supply fails. Following the failure of a power supply, the StackPower mode becomes power sharing.
Note | Power-sharing mode is the recommended configuration for Catalyst 3850 switches. |
For general concepts and management procedures for switch power stacks, see the software stacking configuration guide on Cisco.com.
- A switch power stack can include a maximum of four switches in a ring topology and nine switches in a star topology.
- Size of the switch and any optional power supply module. The 1100-W power-supply module is 1.5 inches (3.81 cm) longer than the other modules, and with the attached cable retention clip, it extends 3 inches (7.62 cm) from the switch chassis. Stacking switches with the same power-supply modules together makes it easier to cable the switches. For switch dimensions, see Appendix A, “Technical Specifications.”
- Length of cable. Depending on the configurations that you have, you might need different-sized cables. If you do not specify the length of the StackPower cable, the 0.3 meter cable is supplied. If you need the 1.5 meter cable, you can order it from your Cisco supplier. For cable part numbers, see StackPower Connector. The StackPower Cabling Configurations provides examples of recommended configurations.
- For rack-mounted switch stacks that are members of a data stack and a StackPower stack, see Switch Stacking and Power Stacking Guidelines.
StackPower Cabling Configurations
This section describes the recommended cabling configurations for a StackPower stack. There are two types of StackPower cables.
The cable is available in two lengths.
| Part Number | Cable Type | Length |
|---|---|---|
| CAB-SPWR-30CM | StackPower Cable | 0.3 meter |
| CAB-SPWR-150CM | StackPower Cable | 1.5 meter |
This figure shows a ring configuration using both of the supplied 0.3-meter StackPower cables and one 1.5-meter cable. In the examples that follow, the switches are stacked in a vertical rack or on a table.
This figure shows nine switches connected in a star topology.
StackPower Partitioning Examples
These figures show StackPower stacks of Catalyst 3850 switches with failover conditions.
In this figure, the StackPower cable 2 is faulty. Therefore, this stack does not provide redundancy.
In this figure, StackPower port B on the center switch has failed and this stack partitions into two stacks. The top two switches share power, and the bottom switch is now a separate stack.
HTH
Regards
Inayath
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