PoE allocation

There are two ways LLDP can negotiate power with a PD:

Using LLDP MED TLVs
Disabled by default. Can be enabled using the int <port-list> PoE-lldp-detect [enable|disable] command, as shown below.LLDP MED TLVs sent by the PD are used to negotiate power only if the LLDP PoE+ TLV is disabled or inactive; if the LLDP PoE+ TLV is sent as well (not likely), the LLDP MED TLV is ignored.
Using LLDP PoE+ TLVs
Enabled by default. The LLDP PoE+ TLV is always advertised unless it has been disabled (enable it by using the lldp config <port-list> dot3TlvEnable poe_config command.)For the Command syntax, see Initiating advertisement of PoE+ TLVs. It always takes precedence over the LLDP MED TLV.

Enabling PoE-lldp-detect allows the data link layer to be used for power negotiation. When a PD requests power on a PoE port, LLDP interacts with PoE to see if there is enough power to fulfill the request. Power is set at the level requested. If the PD goes into power-saving mode, the power supplied is reduced; if the need for power increases, the amount supplied is increased. PoE and LLDP interact to meet the current power demands.

Syntax:


int <port-list> poe-lldp-detect [enabled | disabled]

Allows the data link layer to be used for power negotiation between a PD on a PoE port and LLDP.

Default: Disabled

Example:

You can enter this command to enable LLDP detection:

switch(config) # int 7 PoE-lldp-detect enabled

or in interface context:

switch(eth-7) # PoE-lldp-detect enabled

NOTE:

Detecting PoE information via LLDP affects only power delivery; it does not affect normal Ethernet connectivity.

You can view the settings by entering the show power-over-ethernet brief command, as shown in Port with LLDP configuration information obtained from the device.

Port with LLDP configuration information obtained from the device

switch(config)# show power-over-ethernet brief

 Status and Counters - Port Power Status


  POE   | Power   Power     Alloc Alloc  Actual Configured  Detection   Power
  Port  | Enable  Priority  By    Power  Power  Type        Status      Class
  ----- + ------- --------- ----- ------ ------ ----------- ----------- ----
  A1    | Yes     low       usage 17 W   0.0 W  Phone1      Delivering  1
  A2    | Yes     low       usage 17 W   0.0 W              Searching   0
  A3    | Yes     low       usage 17 W   0.0 W              Searching   0
  A4    | Yes     low       usage 17 W   0.0 W              Searching   0
  A5    | Yes     low       usage 17 W   0.0 W              Searching   0
  A6    | Yes     low       usage 17 W   8.4 W              Delivering  0