Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 811

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 define 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 configuration 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 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, like the power-inline priority, can be Critical, High, or Low. If the Dell Networking OS still finds 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 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 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 Affect of a Port on the Power Budget The PoE and PoE+ power budget is affected differently depending on how you enable PoE and PoE+ and whether a device is connected. The following lists these differences. 1. When you configure 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 configure 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. Power over Ethernet (PoE) 811