LLDP (Link Layer Discovery Protocol) Media Endpoint Discovery (MED) is an extension to LLDP that is published as standard ANSI/TIA-1057. LLDP MED TLVs advertise and receive information for endpoint devices, which can include powered device (PD) information. Some TLVs are advertised by the switch, and some are advertised by the endpoint device.
LLDP MED TLVs
| Name | Comments |
|---|---|
| LLDP MED capabilities | The switch uses this TLV to
advertise the switch LLDP MED capabilities to endpoint devices. This TLV must be configured for advertisement before any other LLDP MED TLVs can be configured for advertisement, and advertisement for all other MED TLVs, must be disabled before advertisement for this TLV can be disabled. |
| Network policy | The switch uses this TLV to
advertise network policy information for specific applications to
endpoint devices. Note: Network
policies cannot be configured by SNMP (Simple Network Management Protocol)-based management programs.
|
| Location ID | The switch uses this TLV to advertise a location ID to an endpoint device. |
| Extended power via MDI | The switch uses this TLV to advertise a power information and settings to an endpoint device on a PoE (Power over Ethernet)-capable port. |
| Hardware revision | An endpoint device uses this TLV to advertise the configured hardware revision to the switch. |
| Firmware revision | An endpoint device uses this TLV to advertise the configured firmware revision to the switch. |
| Software revision | An endpoint device uses this TLV to advertise the configured software revision to the switch. |
| Serial number | An endpoint device uses this TLV to advertise the configured serial number to the switch. |
| Manufacturer name | An endpoint device uses this TLV to advertise the configured manufacturer name to the switch. |
| Model name | An endpoint device uses this TLV to advertise the configured model name to the switch. |
| Asset ID | An endpoint device uses this TLV to advertise the configured asset ID to the switch. |
You must enable the LLDP-MED capabilities TLV for advertising before you configure any other LLDP MED TLVs for advertising. Likewise, when disabling LLDP MED TLV advertisement, you can disable the LLDP-MED capabilities TLV only after you have disabled advertisement for all other LLDP MED TLVs.
After the LLDP-MED capabilities TLV is configured for advertising, the switch can receive LLDP MED TLVs from endpoints; you do not have to configure the switch to receive individual TLVs.
The switch advertises LLDP MED TLVs only after the switch receives an LLDP MED TLV from an endpoint, and the switch only advertises on ports from which an LLDP MED TLV has been received. This approach prevents the switch from advertising LLDP MED TLVs to another switch, and it prevents the wasted bandwidth and processing resources that would otherwise occur.
The LLDP MED protocol extension introduces a new feature called MED fast start, which is automatically enabled when the LLDP MED capabilities TLV is configured for advertisement.
When a new LLDP MED-capable endpoint is detected, the switch advertises the configured LLDP MED TLVs every one second for the configured number of times (called the repeat count). This speeds up the initial exchange of LLDP MED capabilities. After the repeat count is reached, the LLDP MED TLVs are advertised at the configured interval.
Note
The fast-start feature is automatically enabled, at the default level of 3, when you enable the LLDP MED capabilities TLV on the port.
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