Reference Guide

Power over Ethernet and Power over Ethernet Plus | 799
static
: Ports configured in static mode reserve a fixed power allocation whether a device is connected or
not. By default 15.4W is allocated for PoE and 30.0W for PoE+, but this is user-configurable with the
max_milliwatts option. No dynamic PoE/PoE+ class detection is performed on static ports, and Extended
Power via MDI TLVs or IEEE 802.3at power-via-mdi TLVs have no effect.
Extended Power-via-MDI TLV
The PD sends three pieces of information in the LLDP-MED Extended Power-via-MDI TLV:
1. Power Requirement: FTOS honors this and uses it for power allocation.
2. Power Priority—Critical, High, or Low: FTOS honors this information and uses it for power priority
calculation.
3. External Power Source: FTOS does not use this information.
IEEE 802.3at power-via-mdi TLV
The PD sends five pieces of information in the IEEE 802.3at power-via-mdi TLV:
1. Power Class: FTOS honors and displays it in the
show power inline EXEC command (the PD requested
power value must be within the class max watts limit).
2. Type: FTOS honors this request only when it is Type1 or Type2 PD and displays it in the
show power
inline
EXEC command. It does not honor Type1 or Type2 PSE requests.
3. Priority: FTOS honors this and uses it for priority calculation
4. PD requested power value: FTOS honors this and uses it for power allocation.
5. PSE allocated power value: FTOS honors this and uses it to check whether the PD is in sync with the
PSE.
Determine the Affect of a Port on the Power Budget
The PoE/PoE+ power budget is affected differently depending on how PoE/PoE+ is enabled and whether a
device is connected:
1. When you configure a port with
power inline auto without the max_milliwatts power limit option, power
is only allocated after you connect a device to the port.
• When you connect a device, the maximum power for the device class is allocated if there is
sufficient power in the budget. See Table 36-1.
• If there is not enough power in the budget, the configuration is maintained and the port waits for
power to become available.
• If the device advertises its power requirement through LLDP-MED, then FTOS allocates the
required amount and returns the remaining amount to the budget.
Note: LLDP-MED TLVs or IEEE 802.3at power-via-mdi TLVs are only honored if the port is configured
with power inline auto (with or without the max_milliwatts option).