TxRx mode. A port in this mode sends and receives LLDP frames.
Tx mode. A port in this mode only sends LLDP frames.
Rx mode. A port in this mode only receives LLDP frames.
Disable mode. A port in this mode does not send or receive LLDP frames.
Each time the LLDP operating mode of a port changes, its LLDP protocol state machine re-initializes. To
prevent LLDP from being initialized too frequently at times of frequent operating mode change, an
initialization delay, which is user configurable, is introduced. With this delay mechanism, a port must
wait for the specified interval before it can initialize LLDP after the LLDP operating mode changes.
Transmitting LLDP frames
An LLDP-enabled port operating in TxRx mode or Tx mode sends LLDP frames to its directly connected
devices both periodically and when the local configuration changes. To prevent the network from being
overwhelmed by LLDP frames at times of frequent local device information change, an interval is
introduced between two successive LLDP frames.
This interval is shortened to 1 second in either of the following two cases:
A new neighbor is discovered, that is, a new LLDP frame is received carrying device information
new to the local device.
The LLDP operating mode of the port changes from Disable/Rx to TxRx or Tx.
This is the fast sending mechanism of LLDP. With this mechanism, a specific number of LLDP frames
are sent successively at the 1-second interval to help LLDP neighbors discover the local device as soon
as possible. Then, the normal LLDP frame transmit interval resumes.
Receiving LLDP frames
An LLDP-enabled port operating in TxRx mode or Rx mode checks the TLVs carried in every LLDP
frame it receives for validity violation. If valid, the information is saved and an aging timer is set for it
based on the time to live (TTL) value in the TTL TLV carried in the LLDPDU. If the TTL value is zero, the
information is aged out immediately.
Protocols and Standards
The protocols and standards related to LLDP include:
IEEE 802.1AB-2005, Station and Media Access Control Connectivity Discovery
ANSI/TIA-1057, Link Layer Discovery Protocol for Media Endpoint Devices
LLDP Configuration Task List
Complete these tasks to configure LLDP:
Setting LLDP Operating Mode
Setting the LLDP Re-Initialization Delay
Enabling LLDP Polling
Configuring the TLVs to Be Advertised
Configuring the Management Address and Its Encoding Format