H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 349)

31-2
Sending LLDPDUs
An LLDP-enabled device operating in the TxRx mode or Tx mode sends LLDPDUs to its directly
connected devices periodically. It also sends LLDPDUs when the local configuration changes to inform
the neighboring devices of the change timely. In any of the two cases, an interval exists between two
successive operations of sending LLDPDUs. This prevents the network from being overwhelmed by
LLDPDUs even if the LLDP operating mode changes frequently.
To enable the neighboring devices to be informed of the existence of a device or an LLDP operating
mode change (from the disable mode to TxRx mode, or from the Rx mode to Tx mode) timely, a device
can invoke the fast sending mechanism. In this case, the interval to send LLDPDUs changes to one
second. After the device sends specific number of LLDPDUs, the interval restores to the normal. (A
neighbor is discovered when a device receives an LLDPDU and no information about the sender is
locally available.)
Receiving LLDPDUs
An LLDP-enabled device operating in the TxRx mode or Rx mode checks the TLVs carried in the
LLDPDUs it receives and saves the valid neighboring information. An LLDPDU also carries a TTL (time
to live) setting with it. The information about a neighboring device maintained locally ages out when the
corresponding TTL expires.
The TTL of the information about a neighboring device is determined by the following expression:
TTL multiplier × LLDPDU sending interval.
You can set the TTL by configuring the TTL multiplier. Note that the TTL can be up to 65535 seconds.
TTLs longer than it will be rounded off to 65535 seconds.
TLV Types
TLVs encapsulated in LLDPDUs fall into these categories: basic TLV, organization defined TLV, and
MED (media endpoint discovery) related TLV. Basic TLVs are the base of device management.
Organization specific TLVs and MED related TLVs are used for enhanced device management. They
are defined in standards or by organizations and are optional to LLDPDUs.
Basic LLDP TLVs
Table 31-1 lists the basic LLDP TLV types that are currently in use.