H3C Technologies H3C S5560 Series Switches - Manual (Page 273)

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• Disable mode—An LLDP agent in this mode cannot send or receive LLDP frames.
Each time the LLDP operating mode of an LLDP agent 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, an LLDP agent must wait the
specified amount of time to initialize LLDP after the LLDP operating mode changes.
Transmitting LLDP frames
An LLDP agent 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, LLDP uses the token bucket
mechanism to rate limit LLDP frames. For more information about the token bucket mechanism, see ACL
and QoS Configuration Guide.
LLDP automatically enables the fast LLDP frame transmission mechanism in either of the following cases:
• A new neighbor is discovered. A new LLDP frame 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, the specified number of LLDP frames are sent successively at a configurable fast
transmission interval to help LLDP neighbors discover the local device as soon as possible. Then, the
normal LLDP frame transmission interval resumes.
Receiving LLDP frames
An LLDP agent operating in TxRx mode or Rx mode confirms the validity of TLVs carried in every received
LLDP frame. If the TLVs are valid, the LLDP agent saves the information and starts an aging timer. 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
• IEEE 802.1AB-2009, Station and Media Access Control Connectivity Discovery
• ANSI/TIA-1057, Link Layer Discovery Protocol for Media Endpoint Devices
• DCB Capability Exchange Protocol Specification Rev 1.00
• DCB Capability Exchange Protocol Base Specification Rev 1.01
• IEEE Std 802.1Qaz-2011, Media Access Control (MAC) Bridges and Virtual Bridged Local Area
Networks-Amendment 18: Enhanced Transmission Selection for Bandwidth Sharing Between Traffic
Classes