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Disable: the port cannot transmit or receive LLDPDUs.
2) LLDPDU transmission mechanism
If the ports are working in TxRx or Tx mode, they will advertise local information by
sending LLDPDUs periodically.
If there is a change in the local device, the change notification will be advertised. To
prevent a series of successive LLDPDUs transmissions during a short period due to
frequent changes in local device, a transmission delay timer is set by network
management to ensure that there is a defined minimum time between successive LLDP
frame transmissions.
If the LLDP admin status of the port is changed from Disable/Rx to TxRx/Tx, the Fast
Start Mechanism will be active, the transmit interval turns to be 1 second, several
LLDPDUs will be sent out, and then the transmit interval comes back to the regular
interval.
3) LLDPDU receipt mechanism
When a port is working in TxRx or Rx mode, the device will check the validity of the received
LLDPDUs and the attached TLVs, save this neighbor information to the local device and then
set the aging time of this information according to the TTL value of TTL (Time To Live) TLV.
Once the TTL is 0, this neighbor information will be aged out immediately.
The aging time of the local information in the neighbor device is determined by TTL. Hold
Multiplier is a multiplier on the Transmit Interval that determines the actual TTL value used in an
LLDPDU. TTL = Hold Multiplier * Transmit Interval.
TLV
TLV refers to Type/Length/Value and is contained in a LLDPDU. Type identifies what kind of
information is being sent, Length indicates the length of information string in octets and Value is
the actual information to be sent. The basic TLV Format is shown as follows:
Each TLV is identified by a unique TLV type value that indicates the particular kind of information
contained in the TLV.
The following table shows the details about the currently defined TLVs.
TLV Type TLV Name Description Usage in
LLDPDU
0 End of LLDPDU Mark the end of the TLV sequence in LLDPDUs.
Any information following an End Of LLDPDU
TLV shall be ignored.
Mandatory
1 Chassis ID Identifies the Chassis address of the connected
device.
Mandatory
2 Port ID Identifies the MAC address of the specific port
that transmitted the LLDP frame.
Mandatory
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