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How LLDP Works
Transmitting LLDPDUs
An LLDP-enabled port operating in TxRx mode or Tx mode sends LLDPDUs to its directly connected
devices both periodically and when the local configuration changes. To prevent the network from being
overwhelmed by LLDPDUs at times of frequent local device information change, an interval is
introduced between two successive LLDPDUs.
This interval is shortened to 1 second in either of the following two cases:
z A new neighbor is discovered, that is, a new LLDPDU is received carrying device information new
to the local device.
z 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 LLDPDUs are
sent successively at the 1-second interval to help LLDP neighbors discover the local device as soon as
possible. Then, the normal LLDPDU transmit interval resumes.
Receiving LLDPDUs
An LLDP-enabled port operating in TxRx mode or Rx mode checks the TLVs carried in every LLDPDU
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) TLV carried in the LLDPDU. If the TTL TLV is zero, the information is aged out
immediately.
Protocols and Standards
The protocols and standards related to LLDP include:
z IEEE 802.1AB-2005, Station and Media Access Control Connectivity Discovery
z ANSI/TIA-1057, Link Layer Discovery Protocol for Media Endpoint Devices
LLDP Configuration Task List
Complete these tasks to configure LLDP:
Task Remarks
Enabling LLDP Required
Setting LLDP Operating Mode Optional
Setting the LLDP Re-Initialization Delay Optional
Enabling LLDP Polling Optional
Configuring the TLVs to Be Advertised Optional
Configuring the Management Address and Its
Encoding Format
Optional
Setting Other LLDP Parameters Optional
Performing
Basic LLDP
Configuration
Setting the Encapsulation Format for LLDPDUs Optional
Configuring CDP Compatibility Optional
Configuring LLDP Trapping
Optional
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