Administrator Guide

For a complete listing of all PoE commands, see the Dell Networking OS Command Line Reference Guide.
Manage Ports using Power Priority and the Power
Budget
The allocation and return of power-on ports depends on the total inline power available in the system and the power priority calculation.
Determining the Power Priority for a Port
The Dell Networking OS uses a sophisticated port prioritization algorithm to determine which ports receive power so that the PoE and PoE
+ ports are powered up and down deterministically.
The Dell Networking OS maintains a sorted list of PoE and PoE+ ports based on these four parameters. To dene the power priority for a
port, the Dell Networking OS uses the following four parameters, in order:
1 Power-inline mode: Class or Static
NOTE: Static ports have a higher weight than Class mode ports, so all static ports always stay on top of all class ports,
regardless of the other three parameters.
2 Power inline priority conguration
3 Link layer discovery protocol-media endpoint discovery (LLDP-MED) priority the power device (PD) sends in the Extended Power-
via-medium dependent interface (MDI) type, length, value (TLV) or the priority the PD sends in the IEEE 802.3at power-via-MDI TLV
4 Port’s number
Within the set of static ports, the Dell Networking OS attempts to order the ports based on the second parameter, power inline priority, the
default of which is Low. If the Dell Networking OS nds multiple ports with the same power-inline priority, it breaks the tie using the third
parameter, the LLDP-MED Priority or power-via-mdi priority the PD advertises, which, like the power-inline priority, can be Critical,
High, or Low. If the Dell Networking OS still nds a tie, priority is based on the fourth parameter, which is the ports position in the port
extender; there cannot be a tie based on this parameter.
The Dell Networking OS dynamically sorts this list when:
• The power-inline mode or priority changes.
• The PD advertises a dierent LLDP-MED priority or power-via-mdi priority
• The PD is connected or disconnected
The Dell Networking OS always uses this sorted list of ports for allocation. When you add an extra PSU, additional ports are powered based
on this list. If you remove a power supply unit (PSU), this same list is used to remove power from the lowest priority ports.
Determining the Aect of a Port on the Power Budget
The PoE and PoE+ power budget is aected dierently depending on how you enable PoE and PoE+ and whether a device is connected.
The following lists these dierences.
1 When you congure a port as power inline without setting the max_milliwatts power limit option, the Dell Networking OS
does not allocate any power to the port unless a device is connected and there is no limit to the amount of power consumed by the
powered device.
2 When you congure a port aspower inline with the max_milliwatts power limit option, the Dell Networking OS does not
allocate any power to the port unless a device is connected but restricts the maximum power that can be consumed by the powered
device to the amount set through the max_milliwatts option.
3 The max_milliwatts option has no eect on a port extender (PE) port when the PE port is congured to be in Class mode.
786
Power over Ethernet (PoE)