Power over Ethernet
Power over Ethernet (PoE) is a technique for delivering DC power to devices over copper Ethernet cabling, eliminating the need for separate power supplies and outlets. Using PoE can improve flexible options for placing Ethernet end devices, and reduce the time and expense of installing electrical cabling.
PoE is supported on two Cisco Catalyst IE3100 Rugged Series Switch models beginning in the Cisco IOS XE 17.15.x release: IE-3100-4P2S-E and IE-3100-8P2C-E.
For details of PoE support, see PoE Support for Cisco Catalyst IE3100 Rugged Series Switches in this guide.
An IE3100 PoE-capable switch port automatically supplies power to one of these connected devices if the switch senses that there is no power in the circuit:
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An IEEE standard powered device, such as a new Cisco IP phone.
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An IEEE 802.3af-compliant powered device, which can receive up to 15.4 W of DC power
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An IEEE 802.3at-compliant powered device, which can receive up to 30 W of DC power
PoE Support for Cisco Catalyst IE3100 Rugged Series Switches
The following table lists the Cisco Catalyst IE3100 Rugged Series Switches that are supported for PoE.
|
Switch Model |
Supported Ports |
PoE Budget |
|---|---|---|
|
IE-3100-4P2S-E |
Up to 30 W PoE+ output on 4 downlink ports |
120 W |
|
IE-3100-8P2C-E |
Up to 30 W PoE+ output on 8 downlink ports |
240 W |
These switches support the following PoE features in the Cisco IOS XE 17.15.x release:
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PoE power policing:When power policing is enabled, the device polices power usage by comparing the real-time power consumption with the maximum power allocated to the device.
For more information, see the section Power Monitoring and Power Policing.
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Perpetual PoE: Perpetual PoE provides uninterrupted power to a connected powered device even when the power sourcing equipment switch is booting.
For more information, see the section Configuring Perpetual PoE and Fast POE.
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Fast PoE: Fast PoE enables the quick start of PoE power after a system power loss and recovery. If Fast PoE is enabled, the status of the PoE ports is stored in flash memory so that if there is a power loss and recovery, ports can be powered on as quickly as possible.
For more information, see the section Configure Perpetual PoE and Fast PoE.
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PoE Foldback: PoE Foldback is the process in which the system shuts down PoE devices when the primary power source fails, and the standby power source that takes over is of a lower VDC than the primary power source. When the input VDC decreases because the standby source provides a lower VDC, the PoE budget will be reduced. When this happens the switch first shuts down low-priority devices.
If the switch still lacks power, it shuts down high-priority devices in descending order of port number. You can configure port priority using the power inline port priority CLI command.
For more information, see PoE Foldback and Configure Port Priority.
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PoE Boost: IE3200, IE3300, and IE3400 DIN rail platforms require an external 54V DC power supply for PoE operation. IE3100 PoE integrates a boost power supply that can take 12V or 24V to create 54V for PoE applications. The IE3100 can provide PoE power from 9.6V to 60V.
For more information, see the section PoE Boost.
Powered-Device Detection and Initial Power Allocation
The switch detects an IEEE-compliant powered device when the PoE-capable port is in the no-shutdown state, PoE is enabled (the default), and the connected device is not powered by an AC adapter.
After device detection, the switch determines the device's power requirements based on its type:
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The initial power allocation is the maximum amount of power that a powered device requires. The switch initially allocates this amount of power when it detects and powers the powered device. If the switch receives Cisco Discovery Protocol messages from the powered device and the powered device negotiates power levels with the switch through Cisco Discovery Protocol power-negotiation messages, the initial power allocation might be adjusted.
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The switch classifies the detected IEEE device within a power consumption class. Based on the available power in the power budget, the switch determines if a port can be powered. The following table lists these levels.
Table 1. Power Consumption Classes and Power Levels Power Consumption Class
Maximum Power Level Required from Device
0 (class status unknown)
15.4 W
1
4 W
2
7 W
3
15.4 W
4
30 W
IE-3100-4P2S-E and IE-3100-8P2C-E support power consumption classes 1 through 4 (4 W to 30 W).
1-Event Classification
The PoE+ standard (802.3at) uses 2-event classification. This enables the PD to classify itself and receive up to 30W, based on the advertised class, even before the link comes up. By default, 2-event classification is in effect on all interfaces.
The PoE standard (802.3af) uses 1-event classification. If a PD supports only 1-event classification, then the interface on which the PD is connected should be explicitly configured for 1-Event classification. If an interface is configured with 1-event classification, and if the PD returns a value of Class 1, 2, or 3, then the switch provides Class 1, 2, or 3 power, respectively. If the PD returns a value of Class 4, then Class 3 power is provided initially (15.4W is allocated to the PD during start-up, and the PD can renegotiate for more power through CDP/LLDP).
Use the power inline port 1-event command to configure 1-event classification. For example:
IE3100-8P2C#configure terminal
IE3100-8P2C(config)#interface gigabitEthernet 1/3
IE3100-8P2C(config-if)#power inline port 1-event
IE3100-8P2C(config-if)#Power Budget
The switch monitors and tracks requests for power and grants power only when it is available. The switch tracks the power budget (the amount of power available on the device for PoE). The switch also performs power-accounting calculations when a port is granted or denied power to keep the power budget up to date.
After power is applied to the port, the switch uses Cisco Discovery Protocol to determine the Cisco Discovery Protocol-specific power consumption requirement of the connected Cisco powered devices, which is the amount of power to allocate based on the Cisco Discovery Protocol messages. The switch adjusts the power budget accordingly. Note that Cisco Discovery Protocol does not apply to third-party PoE devices. The switch processes a request, and either grants or denies power. If the request is granted, the switch updates the power budget. If the request is denied, the switch ensures that the power to the port is turned off, generates a syslog message, and updates the LEDs. Powered devices can also negotiate with the switch for more power.
 Note |
The Cisco Discovery Protocol-specific power consumption requirement is referred to as the actual power consumption requirement in the Cisco Catalyst Switches software configuration guides and command references. |
With PoE+, powered devices use IEEE 802.3bt and Link Layer Discovery Protocol (LLDP) power with medium-dependent interface (MDI) type, length, and value descriptions (TLVs) and power-via-MDI TLVs, for negotiating power up to 30 W. Cisco IEEE powered devices can use CDP or the IEEE 802.3 at power-via-MDI power-negotiation mechanism to request power levels up to 30 W.
If the PD does not support LLDP, you can configure with either static or 2-event classification to receive required power according to the PD specification.
If the switch detects a fault caused by an undervoltage, overvoltage, overtemperature, oscillator fault, or short-circuit condition, it turns off power to the port, generates a syslog message, and updates the power budget and LEDs.
Power Management Modes
To configure the overall PoE budget of DIN rail switches, use the global configuration command power inline wattage max <watts for primary PSU> <watts for secondary PSU>. Limiting the PoE budget prevents overdrawing power and exceeding the capacity of the power source.
The ranges for power inline wattage max <watts for primary PSU> and power inline wattage max <watts for secondary PSU> depend on the voltage for primary and secondary PSUs, as shown in the following table.
|
Input Voltage Range |
Max PoE Budget Range |
Default Total PoE Budget |
|---|---|---|
|
9.6V < Input Voltage <= 18V |
4W to 31W |
4W |
|
18V < Input Voltage <= 44V |
4W to 90W |
31W |
|
44V < Input Voltage <= 52.5V |
4W to 120W |
120W |
|
52.5V < Input Voltage <= 60V |
4W to 120W (IE3100-4P2S) / 240W (IE3100-8P2C) |
120W (IE3100-4P2S) / 125W (IE3100-8P2C) |
Note |
The switch also needs power, so it is suggested that you reserve 20 watts for the switch. The power budget for PoE would then be the total power of the PSU minus 20 watts. For example, if the PSU can provide 170W of power, the maximum PoE budget you should configure is 150W. See the Datasheet for actual IE3100 power consumption for switch operation. The 20W referenced here is just an example. |
Note |
For cases where VDC is in range of 18V - 44V, the IE3100 assumes a PSU with 50W capacity. The PoE budget is ~20W less than 50W. Cisco sells a PSU with 50W capacity and outputs 24VDC. |
PoE has the following power-management modes:
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Auto: The auto mode is the default setting. The switch automatically detects if the connected device requires power. If the switch discovers a powered device connected to the port, and if the switch has enough power, it grants power, updates the power budget, and turns on power to the port on a first-come, first-served basis, and updates the LEDs. For LED information, see the Cisco Catalyst IE3100 Rugged Series Switches Hardware Installation Guide.
If the switch has enough power for all the powered devices, they all come up. If enough power is available for all the powered devices connected to the switch, power is turned on to all the devices. If enough PoE is not available, or if a device is disconnected and reconnected while other devices are waiting for power, it cannot be determined which devices are granted or are denied power.
If granting power exceeds the system's power budget, the switch denies power, ensures that power to the port is turned off, generates a syslog message, and updates the LEDs. After power is denied, the switch periodically rechecks the power budget and continues to attempt to grant the request for power.
If a device that is being powered by the switch is then connected to AC power, the switch might continue to power the device. The switch might continue to report that it is still powering the device irrespective of whether the device is being powered by the switch or receiving power from an AC power source.
If a powered device is removed, the switch automatically detects the disconnect and removes power from the port. You can connect a nonpowered device without damaging it.
You can specify the maximum wattage that is allowed on the port. If the IEEE class maximum wattage of the powered device is greater than the configured maximum value, the switch does not provide power to the port. If the switch powers a powered device, but the powered device later requests, through Cisco Discovery Protocol or LLDP messages, more than the configured maximum value, the switch removes power to the port. The power that was allocated to the powered device is reclaimed into the global power budget. If you do not specify a wattage, the switch delivers the maximum value. Use the auto setting on any PoE port.
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Static: The switch preallocates power to the port (even when no powered device is connected) and guarantees that power will be available for the port. The switch allocates the port-configured maximum wattage, and the amount is never adjusted through the IEEE class or by Cisco Discovery Protocol messages from the powered device. Because power is preallocated, any powered device that uses less than or equal to the maximum wattage is guaranteed to be powered when it is connected to the static port. The port no longer participates in the first-come, first-served model.
However, if the powered device's IEEE class is greater than the maximum wattage, the switch does not supply power to it. If the switch learns through Cisco Discovery Protocol messages that the powered device is consuming more than the maximum wattage, the switch shuts down the powered device.
If you do not specify a wattage, the switch preallocates the maximum value. The switch powers the port only if it discovers a powered device.
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Never: The switch disables powered-device detection and never powers the PoE port even if an unpowered device is connected. Use this mode only when you want to make sure that power is never applied to a PoE-capable port, making the port a data-only port.
For most situations, the default configuration (auto mode) works well, providing plug-and-play operation. No further configuration is required. However, configure a PoE port to specify a higher priority, to make it data only, or to specify a maximum wattage to disallow high-power powered devices on a port.
Power Monitoring and Power Policing
When policing of the real-time power consumption is enabled, the switch takes action when a powered device consumes more power than the maximum amount allocated, which is also referred to as the cutoff-power value.
When PoE is enabled, the switch senses and monitors the real-time power consumption of the connected powered device. This is called power monitoring or power sensing. The switch also polices the power usage with the power policing feature.
Power monitoring is backward-compatible with Cisco intelligent power management and CDP-based power consumption. It works with these features to ensure that the PoE port can supply power to a powered device.
The switch senses the real-time power consumption of the connected device as follows:
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The switch monitors the real-time power consumption by individual ports.
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The switch records the power consumption, including peak power usage, and reports this information through the CISCO-POWER-ETHERNET-EXT-MIB.
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If power policing is enabled, the switch polices power usage by comparing the real-time power consumption with the maximum power allocated to the powered device. The maximum power consumption is also referred to as the cutoff power on a PoE port.
If the powered device uses more than the maximum power allocation on the port, the switch can either turn off the power to the port, or can generate a syslog message while still providing power to the device based on the device configuration. By default, power-usage policing is disabled on all the PoE ports.
If error recovery from the PoE error-disabled state is enabled, the switch automatically takes the PoE port out of the error-disabled state after the specified amount of time.
If error recovery is disabled, you can manually re-enable the PoE port by using the shutdown and no shutdown interface configuration commands.
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If policing is disabled, no action occurs when the powered device consumes more than the maximum power allocation on the PoE port, which could adversely affect the device.
If policing is disabled, the powered device can draw a maximum power based on what is allocated by the switch. If the powered device consumes more than what is allocated, the port hits an Imax error and enters a fault condition.
Power Consumption Values
You can configure the initial power allocation and the maximum power allocation on a port. However, these values are the configured values that determine when the device should turn on or turn off power on the PoE port. The maximum power allocation is not the same as the actual power consumption of the powered device. The actual cutoff power value that the device uses for power policing is not equal to the configured power value.
When power policing is enabled, the device polices the power usage at the switch port, where the power consumption is greater than that requested by the device. When you manually set the maximum power allocation, you must consider the power loss over the cable from the switch port to the powered device. The cutoff power is the sum of the rated power consumption of the powered device and the worst-case power loss over the cable.
We recommend that you enable power policing when PoE is enabled on your device. For example, for a Class 1 device, if policing is disabled and you set the cutoff-power value by using the power inline auto max 6300 interface configuration command, the configured maximum power allocation on the PoE port is 6.3 W (6300 mW). The device provides power to the connected devices on the port if the device needs up to 6.3 W. If the CDP power-negotiated value or the IEEE classification value exceeds the configured cutoff value, the device does not provide power to the connected device. After the device turns on the power on the PoE port, the device does not police the real-time power consumption of the device, and the device can consume more power than the maximum allocated amount, which could adversely affect the device and the devices connected to the other PoE ports.
Monitoring Power Status
Use the following show commands to monitor and verify the PoE configuration.
|
Command |
Description |
|---|---|
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show power inline interface-id detail |
Shows detailed PoE output of the interface. |
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show power inline consumption |
Shows the PoE power allocated to devices connected to the interface. |
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show power inline police interface-id detail |
Shows detailed PoE policing information of the interface. |
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show power inline priority |
Shows PoE priority level configured on the interface(s). |
The following is example output for show power inline:
IE3100_POE_4P2S#show power inline
Available:120.0(w) Used:76.2(w) Remaining:43.8(w)
Interface Admin Oper Power Device Class Max
(Watts)
--------- ------ ---------- ------- ------------------- ----- ----
Gi1/3 auto on 15.4 Ieee PD 3 30.0
Gi1/4 static on 30.0 Ieee PD 3 30.0
Gi1/5 auto on 15.4 Ieee PD 3 30.0
Gi1/6 auto on 15.4 Ieee PD 3 30.0
--------- ------ ---------- ---------- ---------- ------ -----
Totals: 4 on 76.2
IE3100_POE_4P2S#
IE3100_POE_4P2S#show power inline consumption
Interface Consumption Admin
Configured Consumption (Watts)
---------- ----------- -------------------
Gi1/3 YES 15.4
Gi1/4 NO 0.0
Gi1/5 NO 0.0
Gi1/6 NO 0.0
IE3100_POE_4P2S#
IE3100_POE_4P2S#
IE3100_POE_4P2S#show power inline police
Available:120.0(w) Used:76.2(w) Remaining:43.8(w)
Interface Admin Oper Admin Oper Cutoff Oper
State State Police Police Power Power
--------- ------ ---------- ---------- ---------- ------ -----
Gi1/3 auto on none n/a n/a 13.2
Gi1/4 static on none n/a n/a 13.0
Gi1/5 auto on none n/a n/a 13.2
Gi1/6 auto on none n/a n/a 13.0
--------- ------ ---------- ---------- ---------- ------ -----
Totals: 52.4
IE3100_POE_4P2S#
IE3100_POE_4P2S#show power inline police gigabitEthernet 1/3
Available:120.0(w) Used:76.2(w) Remaining:43.8(w)
Interface Admin Oper Admin Oper Cutoff Oper
State State Police Police Power Power
--------- ------ ---------- ---------- ---------- ------ -----
Gi1/3 auto on none n/a n/a 13.2
IE3100_POE_4P2S#
IE3100_POE_4P2S#show power inline priority
Interface Admin Oper Admin
State State Priority
---------- ------ ---------- ----------
Gi1/3 auto on low
Gi1/4 static on high
Gi1/5 auto on low
Gi1/6 auto on low
IE3100_POE_4P2S#
PoE Foldback
If the primary power source fails, and the standby power source is providing less VDC input than the primary, the Cisco Catalyst IE3100 Rugged Series Switch shuts down PoE devices, based on port priority. This process is called PoE Foldback and is enabled when you configure the wattages of the external connected power supplies. Use the power inline wattage max <watts for primary PSU> <watts for secondary PSU> command to configure the wattages for primary and secondary power supplies. For details about this command, see Power Management Modes.
Note |
If the power supplies are of same voltage, then their power rating should also be the same. If both the power supplies have the same voltage and same power rating, then both PSUs can handle the power in the switch redundantly and PoE Foldback is not required. However, if the two PSUs have the same voltage but a different power rating, then PoE Foldback is not triggered and the switch might reload. In this case the switch detects a power supply switchover based on the incoming voltage change. Because the voltage is same, the assumption is that the power supplies are the same wattage. Note that PSUs with the same voltage but different wattage is not a supported option. |
When PoE Foldback is in effect, if power from the higher power supply fails, the switch shuts down power to ports with low-priority. If the switch still lacks power then the high-priority ports are shut down in descending order of port number. It does so until power consumption returns to normal.
By default, all powered devices are low priority, but you can configure high priority ports using the power inline port priority CLI command. However, you must change priority before the port has been powered on. If the port is powered on, you must switch it off, change priority, and then switch the port back on.
If the power is restored or a new power supply is added, the switch powers on the devices on a first-come-first-serve basis.
See the section Configure Port Priority for more information.
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