- Index
- Preface
- Overview
- Using the Command-Line Interface
- Assigning the Switch IP Address and Default Gateway
- Configuring Cisco IOS Configuration Engine
- Managing Switch Stacks
- Clustering Switches
- Administering the Switch
- Configuring SDM Templates
- Managing Catalyst 3750-X Stack Power
- Configuring Switch-Based Authentication
- Configuring IEEE 802.1x Port-Based Authentication
- Configuring Web-Based Authentication
- Configuring Interface Characteristics
- Configuring Auto Smartports Macros
- Configuring VLANs
- Configuring VTP
- Configuring Voice VLANs
- Configuring Private VLANs
- Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
- Configuring STP
- Configuring MSTP
- Configuring Optional Spanning-Tree Features
- Configuring Flex Links
- Configuring DHCP Features and IP Source Guard
- Configuring Dynamic ARP Inspection
- Configuring IGMP Snooping and MVR
- Configuring IPv6 MLD Snooping
- Configuring Port-Based Traffic Control
- Configuring CDP
- Configuring LLDP, LLDP-MED, and Wired Location Service
- Configuring UDLD
- Configuring SPAN and RSPAN
- Configuring RMON
- Configuring System Message Logging
- Configuring SNMP
- Configuring Embedded Event Manager
- Configuring Network Security with ACLs
- Configuring IPv6 ACLs
- Configuring QoS
- Configuring EtherChannels
- Configuring TelePresence E911 IP Phone Support
- Configuring IP Unicast Routing
- Configuring IPv6 Unicast Routing
- Configuring HSRP
- Configuring Cisco IOS IP SLAs Operations
- Configuring Enhanced Object Tracking
- Configuring WCCP
- Configuring IP Multicast Routing
- Configuring MSDP
- Configuring Fallback Bridging
- Troubleshooting
- Configuring Online Diagnostics
- Supported MIBs
- Working with the Cisco IOS File System, Configuration Files, and Software Images
- Unsupported Commands in Cisco IOS Release 12.2(53)SE
Configuring Catalyst 3750-X StackPower
The Catalyst 3750-X and 3560-X switches have 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 Catalyst 3750-X stackable 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.
A power stack cannot contain more than four switches. If you merge two stacks, the total number of switches cannot exceed four.
Note StackPower is not supported in switches running the LAN base feature set.
See the hardware installation guide for information on designing and connecting the power stack. For more information about PoE ports, see the “Power over Ethernet Ports” section in the chapter on Configuring Interfaces. For more information about the commands in this chapter, see the command reference for this release.
Understanding StackPower
Some reasons for connecting individual switches in a power stack are:
- In case of power supply failure, if there is enough spare power budget in the rest of the power stack, switches can continue to function.
- You can replace a defective power supply without having to shut down all powered devices in the systems.
- System operation can become more green by maximizing power supply efficiency and working with the most efficient load (30 to 90% of their maximum load).
- 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.
These sections describe stack power:
StackPower Modes
A power stack can run in one of two modes, configured by using the command-line interface:
- 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). To configure power-stack parameters, enter the stack-power stack global configuration command followed by the name of the power stack to enter stack-power configuration mode.
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. This is a switch parameter and is configurable by entering the stack-power switch global configuration command followed by a switch number to enter switch stack power configuration mode.
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 entering the power inline port priority { high | low } interface configuration command. By default, all ports are low priority. This command is visible only on PoE ports.
Note Although the power inline port priority {high | low} command is visible on the Catalyst 3560-X switch PoE ports, it has no effect because Catalyst 3560-X switches do not participate in stack power.
You configure the priority values of each switch in the power stack and of all high and low priority ports on that switch by using the power priority commands in power-stack configuration mode. These commands 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 that case there would be nine members (switches) per system with three priorities per switch. See the hardware installation guide for more information on StackPower star and ring configuration.
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.
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.
- 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.
Immediate Load Shedding Example
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).
The output of the show stack-power privileged EXEC command shows the priorities of the powered devices and switches in the power stack.
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.
Configuring Stack Power
Configuring stack power includes these tasks:
- Identifying a stack ID and setting the power stack mode for the power stack to power sharing or redundant with a strict or non-strict (loose) adherence to the power budget. See the “Configuring Power Stack Parameters” section.
- Configuring switches in the power stack with the power stack ID and setting the priority on PoE ports to high or low. See the “Configuring Power Stack Switch Power Parameters” section.
- Setting priority values for switches in the power stack and for the high and low priority ports on the switch to determine load-shedding order. See the “Configuring PoE Port Priority” section.
Configuring Power Stack Parameters
Beginning in privileged EXEC mode, follow these steps to configure a power stack:
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.
Configuring Power Stack Switch Power Parameters
Beginning in privileged EXEC mode, follow these steps to configure a switch in a power stack:
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.
Note Entering the write erase and reload privileged EXEC commands down not change the power priority or power mode non-default configuration saved in the switch flash memory.
Configuring PoE Port Priority
Beginning in privileged EXEC mode, follow these steps to configure the priority of a PoE port on a switch:
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.