PoE allocation

There are two ways LLDP negotiates power with a PD:

  • Using LLDP MED TLVs

    Disabled by default. Enable using the int <PORT-LIST> PoE-lldp-detect [enabled|disabled] 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 poeplus_config command.)

    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.