Users Guide

Determine the Power Priority
Dell Networking OS uses a sophisticated port prioritization algorithm to determine which ports should receive
power so that the PoE and PoE+ ports are powered up and down deterministically.
Dell Networking OS uses the following four parameters for defining the power priority for a port:
1 Power inline mode: class or static.
2 Power inline priority configuration.
3 LLDP-MED priority sent by the PD in the Extended Power-via-MDI TLV or the priority sent by the PD in
the IEEE 802.3at power-via-mdi TLV.
4 Slot and port number.
Dell Networking OS maintains a sorted list of PoE/PoE+ ports based on the above parameters. The static
ports have higher weight than class mode ports. Hence all static ports always stay on top of all class ports,
regardless of the other parameters. 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 finds 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 can be
Critical,
High, or Low. If the Dell Networking OS still finds a tie, the priority is based on the fourth parameter, which is
the position of the port number in the switch. 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 different 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 power
supply unit (PSU), the additional ports are powered based on this list. If you remove a PSU, the same list is
used to remove power from the ports with lowest priority.
Advertising Extended Power
The power device(PD) sends the information in the LLDP-MED extended power via MDI TLV and information
in the IEEE 802.3 power via MDI TLV.
Dell Networking OS uses the following information sent through LLDP-MED extended power-via-MDI TLV.
The power is advertised using the advertise med power-via-mdi command.
• Power Requirement — Used for power allocation.
• Power Priority — Used for priority calculation. The values are: Critical, High, Low.
• External Power Source — Not used.
Dell Networking OS uses the following information sent through IEEE 802.3 power-via-mdi TLV. The power is
advertised using the advertise dot3-tlv power-via-mdi command.
• Power Class — Displayed in the show power inline EXEC command. The PD-requested power value
must be within the limits of the maximum watts.
• Type — Displayed in the show power inline EXEC command and is used only when the PD is Type1 or
Type2. The Type1 or Type2 PSE requests are not used.
Power over Ethernet (PoE) 697