When using PoE, enabling poe-lldp-detect
allows automatic power configuration if the link partner supports PoE. When LLDP is enabled, the information about the power usage of the PD is available, and the switch can then comply with or ignore this information. You can configure PoE on each port according to the PD (IP phone, wireless device, and so on) specified in the LLDP field. The default configuration is for PoE information to be ignored if detected through LLDP.
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NOTE: Detecting PoE information via LLDP affects only power delivery; it does not affect normal Ethernet connectivity. |
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The data link layer classification DLC for PoE provides more exact control over the power requirement between a PSE and PD. The DLC works in conjunction with the physical layer classification PLC and is mandatory for any Type-2 PD that requires more than 12.95 watts of input power.
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NOTE: DLC is defined as part of the IEEE 802.3at standard. |
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The power negotiation between a PSE and a PD can be implemented at the physical layer or at the data link layer. After the link is powered at the physical layer, the PSE can use LLDP to repeatedly query the PD to discover the power needs of the PD. Communication over the data link layer allows finer control of power allotment, which makes it possible for the PSE to supply dynamically the power levels needed by the PD. Using LLDP is optional for the PSE but mandatory for a Type 2 PD that requires more than 12.95 watts of power.
If the power needed by the PD is not available, that port is shut off.
LLDP can negotiate power with a PD by using LLDP MED TLVs (disabled by default). This can be enabled using the int <
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.port-list
> PoE-lldp-detect [enabled|disabled]
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:
Example:
You can enter this command to enable LLDP detection:
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NOTE: Detecting PoE information via LLDP affects only power delivery; it does not affect normal Ethernet connectivity. |
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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
HP Switch (config)# show power-over-ethernet brief Status and Counters - Port Power Status System Power Status : No redundancy PoE Power Status : No redundancy Available: 300 W Used: 0 W Remaining: 300 W Module A Power Available: 300 W Used: 5 W Remaining: 295 W 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 0.0 W Searching 0
To view information about LLDP port configuration, use the show lldp config
command.
Syntax:
LLDP port configuration information with PoE
HP Switch(config)# show lldp config 4 LLCP Port Configuration Detail Port : 4 AdminStatus [Tx_Rx] : Tx_Rx NotificationsEnabled [False] : False Med Topology Trap Enabled [False] : False TLVS Advertised: * port_descr * system_name * system_descr * system_cap * capabilities * network_policy * location_id * poe * macphy_config * poeplus_config IpAddress Advertised:
Local power information shows an Example: of the local device power information using the show lldp info local-device <
command.port-list
>
Local power information
HP Switch(config)# show lldp info local-device A1 LLCP Local Port Information Detail Port : A1 PortType : local PortId : 1 PortDesc : A1 Pvid : 1 Poe Plus Information Detail Poe Device Type : Type2 PSE Power Source : Primary Power Priority : low PD Requested Power Value : 20 Watts PSE Actual Power Value : 20 Watts
Remote power information shows the remote device power information using the show lldp info remote-device <
command.port-list
>
Remote power information
HP Switch(config)# show lldp info remote-device A3 LLCP Remote Device Information Detail Local Port : A3 ChassisType : mac-address ChassisId : 00 16 35 ff 2d 40 PortType : local PortId : 23 SysName : HPSwitch System Descr : HP Switch 3500-24, revision W.14.xx PortDescr : 23 Pvid : 55 System Capabilities Supported : bridge, router System Capabilities Enabled : bridge Remote Management Address Type : ipv4 Address : 10.0.102.198 Poe Plus Information Detail Poe Device Type : Type2 PD Power Source : Only PSE Power Priority : low PD Requested Power Value : 20 Watts PSE Actual Power Value : 20 Watts
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 08/04/13 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 08/04/13 13:36:31 02771 ports: Port A1 PoE power dropped. Exceeded physical classification due to change in classification type (LLDP process enabled)