Configuring Stack Power
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Configuring Stack Power

This module contains the following sections:

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release.

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Related References

Prerequisites for StackPower

StackPower uses these terms:

  • Available power is the total power available for PoE from all power supplies in the power stack. To see the available power in a stack, enter the show power inline privileged EXEC command.
  • Budgeted power is the power allocated to all powered devices connected to PoE ports in the stack. Budgeted power is referred to as Used (Watts) in the output of the show power inline command.
  • Consumed power is the actual power consumed by the powered devices. Consumed power is typically less that the budgeted power. To see the consumed power in a stack, enter the show power inline police privileged EXEC command.

Restrictions for StackPower

StackPower is not supported in switches running the LAN base feature set.

Information About StackPower

Power Supplies for the Stacking Switch

The switch has two power supplies per system, allowing the power load to be split between them. This accommodates the increased maximum power of 30 watts per port provided to a powered device to meet the PoE+ standard (802.3at). With PoE+, a 48-port system would need 1440 Watts to provide 30 Watts per powered device for the PoE ports. Systems with fewer powered devices might require only one power supply. In this case, the additional power supply can provide one-to-one redundancy for the active supply.

In addition, the stacking switch supports StackPower, which allows the power supplies to share the load across multiple systems in a stack. By connecting the switches with power stack cables, you can manage the power supplies of up to four stack members as a one large power supply that provides power to all switches and to the powered devices connected to switch ports. Since power supplies are most effective when running at 30 to 90% of their maximum load, taking some of the power supplies offline provides maximum power efficiency. Switches in a power stack must be members of the same switch (data) stack.

StackPower Modes

You can configure the power stack to run in one of two modes:

  • In power-sharing mode (the default), all input power is available to be used for power loads. The total available power in all switches in the power stack (up to four) is treated as a single large power supply, with power available to all switches and to all powered devices connected to PoE ports. In this mode, the total available power is used for power budgeting decisions and no power is reserved to accommodate power-supply failures. If a power supply fails, powered devices and switches could be shut down (load shedding).
  • In redundant mode, the power from the largest power supply in the system is subtracted from the power budget, which reduces the total available power, but provides backup power in case of a power-supply failure. Although there is less available power in the pool for switches and powered devices to draw from, the possibility of having to shut down switches or powered devices in case of a power failure or extreme power load is reduced.

In addition, you can configure the mode to run a strict power budget or a non-strict (relaxed) power budget. In both modes, power is denied when there is no more power available in the power budget.

  • In strict mode, when a power supply fails and the available power drops below the budgeted power, the system balances the budget through load shedding of powered devices, even if the actual power being consumed is less than the available power.
  • In non-strict mode, the power stack is allowed to run in an over-allocated state and is stable as long as the actual power does not exceed the available power. In this mode, a powered device drawing more than normal power could cause the power stack to start shedding loads. This is normally not a problem because most devices do not run at full power and the chances of multiple powered devices in the stack requiring maximum power at the same time is small.

You configure power modes at a power-stack level (that is, the mode is the same for all switches in the power stack).

You can also configure a switch connected in a power stack to not participate in the power stack by setting the switch to standalone power mode. This mode shuts down both stack power ports.

Related Tasks
Related References

Power Priority

You can configure the priority of a switch or powered device to receive power. This priority determines the order in which devices are shut down in case of a power shortage. You can configure three priorities per system: the system (or switch) priority, the priority of the high-priority PoE ports on a switch, and the priority of the low-priority PoE ports on a switch.

You set port priority at the interface level for powered devices connected to a PoE port. By default, all ports are low priority.

You configure the priority values of each switch in the power stack and of all high and low priority ports on that switch to set the order in which switches and ports are shut down when power is lost and load shedding must occur. Priority values are from 1 to 27; switches and ports with highest values are shut down first.


Note

The 27 priorities are used to accommodate power stacks connected in a star configuration with the expandable power supply. In this configuration, there would be nine members (switches) per system with three priorities per switch.

On any switch, the switch priority must be lower than port priorities. and the high priority value must be set lower than the low priority value. We recommend that you configure different priority values for each switch and for its high priority ports and low priority ports. This limits the number of devices shut down at one time during a loss of power. If you try to configure the same priority value on different switches in a power stack, the configuration is allowed, but you receive a warning message.

The default priority ranges, if none are configured, are 1-9 for switches, 10-18 for high-priority ports, and 19-27 for low-priority ports.

Related Tasks
Related References

Load Shedding

Load shedding is the process of shutting down devices in case of power supply, cable, or system failures. For power stacks in power-sharing mode, there are two types of load-shedding: immediate and graceful.

  • Immediate load shed occurs when a failure could cause the power stack to fail very quickly. For example, if the largest power supply in the power stack fails, this could cause the stack to immediately start shutting down powered devices.
  • Graceful load-shedding can occur when a smaller power supply fails. Switches and powered devices are shut down in order of their configured priority, starting with devices with priority 27, until the power budget matches the input power.

Graceful load shedding is always enabled and immediate load shedding occurs only when necessary, so both can occur at the same time.


Note

Load shedding does not occur in redundant mode unless two or more power supplies fail, because the largest power supply is used as a backup power source.

Notes on load shedding:

  • The method (immediate or graceful) is not user-configurable, but is based on the power budget.
  • Immediate load shedding also occurs in the order of configured priority, but occurs very quickly to prevent hardware damage caused by loss of power.
  • If a switch is shut down because of load shedding, the output of the show stack-power privileged EXEC command still includes the MAC address of the shut down switch as a neighbor switch, even though the switch is down. This command output shows the StackPower topology, even if there is not enough power to power up a switch.
Related References

How to Configure StackPower

Configuring stack power includes these tasks:

Configuring PowerStack Parameters

SUMMARY STEPS

    1.    configure terminal

    2.    stack-power stack power stack name

    3.    mode {power-sharing | redundant} [strict]

    4.    end

    5.    show stack-power


DETAILED STEPS
     Command or ActionPurpose
    Step 1configure terminal


    Example: 
    Switch# configure terminal
     

    Enters global configuration mode.

     
    Step 2stack-power stack power stack name


    Example: 
    Switch(config)# stack-power stack power 1
     

    Enters the stack power stack name and enter power stack configuration mode. The name can be up to 31 characters.

     
    Step 3mode {power-sharing | redundant} [strict]


    Example: 
    Switch(config-stackpower)# mode redundant
     

    Sets the operating mode for the power stack:

    • power-sharing—The input power from all switches in the power stack can be used for loads, and the total available power appears as one huge power supply. This is the default.
    • redundant—The largest power supply is removed from the power pool to be used as backup power in case one of the other power supplies fails. This is the recommended mode if enough power is available in the system.
    • strict—(Optional) Configures the power stack mode to run a strict power budget. The stack power needs cannot exceed the available power. The default is non-strict.
     
    Step 4end


    Example:
    Switch(config-stackpower)# end
     

    Returns to privileged EXEC mode.

     
    Step 5show stack-power


    Example:
    Switch# show stack-power
     

    Verifies your entries.

     
    Related Concepts
    Related References

    Configuring PowerStack Switch Power Parameters

    SUMMARY STEPS

      1.    configure terminal

      2.    stack-power switch switch-number

      3.    stack [power-stack-name]

      4.    power-priority switch value

      5.    power-priority high value

      6.    power-priority low value

      7.    end

      8.    show stack-power


    DETAILED STEPS
       Command or ActionPurpose
      Step 1configure terminal


      Example: 
      Switch# configure terminal
              		 
      Step 2stack-power switch switch-number


      Example: 
      Switch(config)# stack-power switch 4
       

      Enters global configuration mode.

      Enters switch stack power configuration mode for the stack member switch number. The range is from 1 to 9.

      Note   

      Only four switches can belong to the same power stack.

       
      Step 3stack [power-stack-name]


      Example: 
      Switch(config-switch-stackpower)# stack power2
       

      Enters the name of the power stack to which the switch belongs. The name can be up to 31 characters. If you do not enter a name and no other switches in the power stack have a name configured, a power-stack name is automatically generated.

       
      Step 4power-priority switch value


      Example: 
      Switch(config-switch-stackpower)# power-priority switch 5
       

      Sets the power priority of the switch. The range is from 1 to 27. This value must be lower than the value set for the low and high-priority ports.

       
      Step 5power-priority high value


      Example: 
      Switch(config-switch-stackpower)# power-priority high 12
       

      Sets the power priority of the PoE ports on the switch that are configured as high-priority ports. The range is from 1 to 27, with 1 as the highest priority. The high value must be lower than the value set for the low-priority ports and higher than the value set for the switch.

       
      Step 6power-priority low value


      Example: 
      Switch(config-switch-stackpower)# power-priority low 20
       

      Sets the power priority of the PoE ports on the switch that are configured as low-priority ports. The range is from 1 to 27. This value must be higher than the value set for the high-priority ports and the value set for the switch.

       
      Step 7end


      Example:
      Switch(config-switch-stackpower)# end
       

      Returns to privileged EXEC mode.

       
      Step 8show stack-power


      Example:
      Switch# show stack-power
       

      Verifies your entries.

       
      Related Concepts
      Related References

      Configuring PoE Port Priority

      SUMMARY STEPS

        1.    configure terminal

        2.    interface interface-id

        3.    power inline port priority {high | low}

        4.    end

        5.    show power inline priority


      DETAILED STEPS
         Command or ActionPurpose
        Step 1configure terminal


        Example: 
        Switch# configure terminal
         

        Enters global configuration mode.

         
        Step 2interface interface-id


        Example: 
        Switch(config)# interface gigabitethernet 1/0/1
         

        Enters the interface ID of the port in the stack and enters interface configuration mode. The interface must be a PoE port.

         
        Step 3power inline port priority {high | low}


        Example:
        Switch(config-if)# power inline port priority high
         

        Sets the power priority of the port to high or low. Powered devices connected to low priority ports are shut down first in case of a power reduction. The default is low priority.

        Note   

        Although the power inline port priority {high | low} command is visible on the nonstacking switch PoE ports, it has no effect because these switches do not participate in stack power.

         
        Step 4end


        Example:
        Switch(config-if)# end
         

        Returns to privileged EXEC mode.

         
        Step 5 show power inline priority


        Example:
        Switch# show power inline priority
         

        Verifies your entries.

         
        Related Concepts
        Related References

        Configuration Examples for Stack Power

        Immediate Load Shedding: Examples

        For power stacks in power-sharing mode, if a large power supply in the power stack fails, the stack immediately starts shutting down powered devices until the power budget matches the input power. This example has a power stack of four switches (Powerstack1) in power sharing mode and shows which devices would be shut down in the immediate load shedding process caused by loss of either of two power supplies.

        The output of the show env all command shows that power supplies included in power sharing are a 715 W power supply in switch 1, and one 350 W and one 1100 W power supply in switch 4. Other power supplies are inactive (disabled or not present).

        Switch# show env all
FAN 1 is OK
FAN 2 is OK
FAN PS-1 is OK
FAN PS-2 is OK
TEMPERATURE is OK
Temperature Value: 30 Degree Celsius
Temperature State: GREEN
Yellow Threshold : 49 Degree Celsius
Red Threshold    : 59 Degree Celsius
SW  PID                 Serial#     Status           Sys Pwr  PoE Pwr  Watts
--  ------------------  ----------  ---------------  -------  -------  -----
1A  NG3K-PWR-715WAC     LIT133705FH  OK              Good     Good     715/0
1B  C3KX-PWR-715WAC     DTN1341K018  Disabled        Good     Good     715/0
2A  Not Present
2B  C3KX-PWR-325WAC     LIT13330FNM  Disabled        Good     Good     325/0
3A  C3KX-PWR-325WAC     LIT13330FN3  Disabled        Good     Good     325/0
3B  Not Present
4A  C3KX-PWR-350WAC     DTN1342L00T  OK              Good     Good     350/0
4B  NG3K-PWR-1100WAC    LIT13370577  OK              Good     Good     1100/0

<output truncated>

        The output of the show stack-power privileged EXEC command shows the priorities of the powered devices and switches in the power stack.

        Switch# show stack-power
Power stack name: Powerstack1 
    Stack mode: Power sharing
    Switch 1:
        Power budget: 206
        Low port priority value: 17
        High port priority value: 16
        Switch priority value: 2
        Port A status: Not shut
        Port B status: Not shut
        Neighbor on port A: 0022.bdcf.ab00
        Neighbor on port B: 0022.bdd0.4380

    Switch 2:
        Power budget: 206
        Low port priority value: 12
        High port priority value: 11
        Switch priority value: 1
        Port A status: Not shut
        Port B status: Not shut
        Neighbor on port A: 0022.bdd0.6d00
        Neighbor on port B: 0022.bdcf.af80

    Switch 3:
        Power budget: 656
        Low port priority value: 22
        High port priority value: 21
        Switch priority value: 3
        Port A status: Not shut
        Port B status: Not shut
        Neighbor on port A: 0022.bdcf.af80
        Neighbor on port B: 0022.bdd0.6d00

    Switch 4:
        Power budget: 682
        Low port priority value: 27
        High port priority value: 26
        Switch priority value: 4
        Port A status: Not shut
        Port B status: Not shut
        Neighbor on port A: 0022.bdd0.4380
        Neighbor on port B: 0022.bdcf.ab00

        If the 715 W or 1100 W power supply fails, devices (powered devices connected to PoE ports and the switches themselves) would be shut down in the this order until power consumption drops below 105% of the rated power of the remaining power supplies:

        • Devices connected to Switch 4 low priority ports (priority 27)
        • Devices connected to Switch 4 high priority ports (priority 26)
        • Devices connected to Switch 3 low priority ports (priority 22)
        • Devices connected to Switch 3 high priority ports (priority 21)
        • Devices connected to Switch 1 low priority ports (priority 17)
        • Devices connected to Switch 1 high priority ports (priority 16)
        • Devices connected to Switch 2 low priority ports (priority 12)
        • Devices connected to Switch 2 high priority ports (priority 11)
        • Switch 4 (priority 4)
        • Switch 3 (priority 3)
        • Switch 1 (priority 2)

        Switch 2 would never have to be shut down because all power would have been lost by the time priority 1 devices were reached.

        The output from the show stack-power load-shedding order command shows the order in which devices would shut down in the event of load-shedding:

        Switch# show stack-power load-shedding order powerstack-1
Power Stack           Stack   Stack    Total   Rsvd    Alloc   Unused  Num  Num
Name                  Mode    Topolgy  Pwr(W)  Pwr(W)  Pwr(W)  Pwr(W)  SW   PS
--------------------  ------  -------  ------  ------  ------  ------  ---  ---
Powerstack-1          SP-PS   Ring     2880    34      473     2373    2    4

Priority    Load  Switch or PoE
Shed Order  Type  Devices Shed
----------  ----  ------------------------------------------------------------
22          Lo    Gi2/0/16,
21          Lo    Gi1/0/13, Gi1/0/20,
12          Hi    Gi1/0/7,
4           Sw    Switch: 2
3           Sw    Switch: 1
        Related Concepts

        Configuring PowerStack Parameters: Example

        This is an example of setting the stack power mode for the stack named power1 to redundant power mode. The largest power supply in the stack is removed from the power budget and used as a backup in case of power supply failure. 

        Switch(config)# stack-power stack power1 
Switch(config-stackpower)# mode redundant
Switch(config-stackpower)# exit
        Related Concepts
        Related Tasks

        Configuring PowerStack Switch Power Parameters: Example

        This is an example of setting the switch stack power parameters for switch 3 in the stack that is connected to the power stack with the stack ID power2. If load-shedding becomes necessary, switches and powered devices in the power stack with the higher numbers are shut down first, with shutdown proceeding in order.

        Switch(config)# stack-power switch 3
Switch(config-switch-stackpower)# stack power2
Switch(config-switch-stackpower)# power-priority switch 5
Switch(config-switch-stackpower)# power-priority high 12
Switch(config-switch-stackpower)# power-priority low 20
Switch(config-switch-stackpower)# exit
Switch(config-stackpower)# exit

        Note

        Entering the write erase and reload privileged EXEC commands do not change the power priority or power mode non-default configuration saved in the switch flash memory.

        Related Concepts
        Related Tasks

        Configuring PoE Port Priority: Example

        This is an example of setting the power priority of a port to high so that it is one of the last ports to shut down in case of a power failure.

        Switch(config)# interface gigabitetherent1/0/1
Switch(config-if)# power inline port priority high
Switch(config-if)# exit
        Related Concepts
        Related Tasks

        Where to Go Next

        See the hardware installation guide for information
        • Designing and connecting the power stack.
        • StackPower star and ring configuration

        Additional References for StackPower

        MIBs

        MIB MIBs Link

        All supported MIBs for this release.

        To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

        http:/​/​www.cisco.com/​go/​mibs

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