H3C Technologies H3C S12500-X Series Switches - Manual (Page 168)

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NOTE:
If the MAC/PHY configuration/status TLV is not advertisable, none of the LLDP-MED TLVs will be
advertised even if they are advertisable. If the LLDP-MED capabilities TLV is not advertisable, the other
LLDP-MED TLVs will not be advertised even if they are advertisable.
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.
Work mechanism
LLDP operating modes
An LLDP agent can operate in one of the following modes:
• TxRx mode—An LLDP agent in this mode can send and receive LLDPDUs.
• Tx mode—An LLDP agent in this mode can only send LLDPDUs.
• Rx mode—An LLDP agent in this mode can only receive LLDPDUs.
• Disable mode—An LLDP agent in this mode cannot send or receive LLDPDUs.
Each time the LLDP operating mode of an LLDP agent changes, its LLDP protocol state machine
re-initializes. A configurable re-initialization delay prevents frequent initializations because of frequent
changes to the operating mode. With this delay configured, before an LLDP agent can initialize LLDP, it
must wait for the specified interval after the LLDP operating mode changes.
Transmitting LLDPDUs
An LLDP agent operating in TxRx mode or Tx mode sends LLDPDUs to its directly connected devices both
periodically and when the local configuration changes. To prevent LLDPDUs from overwhelming the
network during times of frequent changes to local device information, LLDP uses the token bucket
mechanism to rate limit LLDPDUs. For more information about the token bucket mechanism, see ACL and
QoS Configuration Guide.
LLDP automatically enables the fast LLDPDU transmission mechanism in either of the following cases:
• A new neighbor is discovered. A new LLDPDU is received and carries device information new to the
local device.
• The LLDP operating mode of the LLDP agent changes from Disable or Rx to TxRx or Tx.
With this mechanism, a specific number of LLDPDUs are sent successively at a configurable fast
transmission interval to help LLDP neighbors discover the local device as soon as possible. Then, the
normal LLDPDU transmit interval resumes.
Receiving LLDPDUs
An LLDP agent that is operating in TxRx mode or Rx mode checks the validity of TLVs carried in every
received LLDPDU. If valid, the information is saved and an aging timer is set for it based on the TTL value
in the TTL TLV carried in the LLDPDU. If the TTL value is zero, the information ages out immediately.
Protocols and standards
• IEEE 802.1AB-2005, Station and Media Access Control Connectivity Discovery