KB.15.15

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.

Operation Note

The advertisement of power with TLVs for LLDP PoE+ is enabled by default. If LLDP is disabled at

runtime and a PD is using PoE+ power that has been negotiated through LLDP, there will be a

temporary power drop. The port will begin using PoE+ power through the PLC. This event is recorded

in the event log. An example message would look like the following:

W 08/04/10 13:35:50 02768 ports: Port A1 PoE power dropped. Exceeded physical classification for a PoE Type1

device (LLDP process disabled)

When LLDP is enabled again, it causes a temporary power drop. This event is also recorded in

the event log. An example message looks like the following:

W 08/04/10 13:36:31 02771 ports: Port A1 PoE power dropped. Exceeded physical classification due to change in

classification type (LLDP process enabled)

About PoE/PoE+ allocation using LLDP information 129