Lldp Operating Modes; Working Mechanism; Protocols And Standards - HP FlexNetwork NJ5000 User Manual

For more information about LLDPDU TLVs, see the IEEE standard (LLDP) 802.1AB-2005 and
the LLDP-MED standard (ANSI/TIA-1057).
Management address
The network management system uses the management address of a device to identify and manage
the device for topology maintenance and network management. The management address is
encapsulated in the management address TLV.

LLDP operating modes

LLDP can operate in one of the following modes:
•
TxRx mode—A port in this mode can send and receive LLDP frames.
•
Tx mode—A port in this mode can only send LLDP frames.
•
Rx mode—A port in this mode can only receive LLDP frames.
•
Disable mode—A port in this mode cannot send or receive LLDP frames.
Each time the LLDP operating mode of a port changes, its LLDP protocol state machine reinitializes.
A configurable reinitialization delay prevents frequent initializations caused by frequent changes to
the operating mode. If you configure the reinitialization delay, a port must wait the specified amount
of time to initialize LLDP after the LLDP operating mode changes.

Working mechanism

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 LLDP
frames from overwhelming the network during times of frequent changes to local device information,
an interval is introduced between two successive LLDP frames.
This interval is shortened to 1 second in either of the following cases:
•
A new neighbor is discovered. A new LLDP frame is received carrying device information new to
the local device.
•
The LLDP operating mode of the port changes from Disable or Rx to TxRx or Tx.
This is the fast sending mechanism of LLDP. With this mechanism, the specified number of LLDP
frames is sent successively at the 1-second interval. The mechanism helps LLDP neighbors
discover the local device as soon as possible. Then, the normal LLDP frame transmission interval
resumes.
Receiving LLDP frames
An LLDP-enabled port operating in TxRx mode or Rx mode confirms the validity of TLVs carried in
every received LLDP frame. If the TLVs are valid, the information is saved and an aging timer is set.
When the TTL value in the Time to Live TLV carried in the LLDP frame becomes zero, the information
ages out immediately.

Protocols and standards

•
IEEE 802.1AB-2005, Station and Media Access Control Connectivity Discovery
•
ANSI/TIA-1057, Link Layer Discovery Protocol for Media Endpoint Devices
176