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Power over Ethernet | 791
Determine the Affect of a Port on the Power Budget
The PoE power budget is affected differently depending on how 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 on page 785.
• 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.
2. When you configure a port with
power inline auto with the power limit option max_milliwatts, power is
only allocated after you connect a device to the port.
• If the maximum power for the device class is less than the power limit you specified, FTOS
allocates the required amount and returns the remaining amount to the budget.
• If there is not enough power in the budget, the configuration is maintained and the port waits for
power to become available.
• If the maximum power for the device class is more than than the power limit you specified, FTOS
does not allocate any power.
3. When you configure a port with
power inline static without the power limit option (max_milliwatts),
FTOS allocates 15.4W (subject to availability and priority) to the port whether or not a device is
connected.
4. When you configure a port with
power inline static with the power limit option (max_milliwatts), FTOS
allocates the specified number of Watts.
• If there is not enough power in the budget, the configuration is maintained and port waits for
power to become available.
• If the maximum power for the device class is more than than the power limit you specified, FTOS
does not allocate any power.
Note: LLDP-MED TLVs are only honored if the port is configured with power inline auto (with or without
the
max_milliwatts option).
Note: When a port is configured with power inline auto (with or without the max_milliwatts option) and the
PoE device is disconnected, the allocated power is returned to the power budget.