Calculate the number of PFC frames required to enable full backpressure on an interface

The priority of the VGMP group is lowered by 2 only when: -A physical interface in the VGMP group fails. -An Eth-Trunk interface in the VGMP group fails. The failure of a member interface of the Eth-Trunk does not affect the priority of the VGMP group. -A member interface of the VGMP group in a VLAN fails. -A member interface of an IP-Link fails.

Enable or disable the PoE function on S series switches:

1. By default, the PoE function is enabled on an interface
2. Enable or disable PoE power supply.
<HUAWEI>system-view
[HUAWEI]interface gigabitethernet 1/0/0
[HUAWEI-GigabitEthernet1/0/0]undo poe enable  //Disable PoE power supply.
[HUAWEI-GigabitEthernet1/0/0]poe enable       //Enable PoE power supply.

The downlink electrical interfaces of PoE switches support PoE power supply, with up to 30 W power on each interface. The maximum power supply distance is 100 m.
Only ES0D0G48VA00 (S7700)/LE0DG48VEA00 (S9300) cards of modular switches (S7700/S9700/S9300/S12700) support PoE power supply.

If the switch connects to 48 V standard PoE powered devices but cannot negotiate power supply capabilities with the devices, you can run poe force-power on the interfaces to forcibly power on the devices.

Priority-based Flow Control (PFC) is a flow control mechanism based on priority. After the data center bridging (DCB) function is enabled on a switch and negotiation succeeds, the switch stops sending packets in the corresponding priority queue when it receives PFC frames. Backpressure timer value = 512 x Time(n)/Interface bandwidth Time(n) indicates the backpressure timer value. The unit is the time an interface uses to send 521 bits.

You can use Hardware Configuration Tool to calculate the number of power modules required in a CE12800 switch. The calculator is also integrated in the UniSTAR system. You can also use the following method to calculate the number of power modules required: Minimum number of power modules required = Sum of maximum power consumption of all working modules in the switch/Maximum power of a single power module + 1 For example, a CE12808 switch uses 2700 W AC power modules and is configured with two CE-CMUAs, five CE-SFU08As, two CE-MPUAs, and two CE-L48XS-EC line cards. Based on the power consumption values of the cards provided in the "Card" section of the CloudEngine 12800 Series Switches Hardware Description and the power consumption of the chassis (including fans) and power modules, the sum of maximum power consumption of all modules can be obtained: 2519 W. Therefore, a minimum of one 2700 W power module is required. To ensure power reliability of a CE12800 switch, it is recommended that you use the N+N backup mode with double power supply systems so that the failure of a single power supply system will not cause power failure or restart of the switch. In the preceding example, the 1+1 backup mode is recommended.