1182 CHAPTER 92: LLDP CONFIGURATION
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 91 lists the basic LLDP TLV types that are currently in use.
Table 91 Basic LLDP TLVs
Type Description Remarks
End of LLDPDU TLV Marks the end of an LLDPDU. Required for
LLDP
Chassis ID TLV Carries the bridge MAC address of the sender
Port ID TLV Carries the sending port. For devices that do
not send MED TLVs, port ID TLVs carry sending
port name. For devices that send MED TLVs,
port ID TLVs carry the MAC addresses of the
sending ports or bridge MAC addresses (if the
MAC addresses of the sending ports are
unavailable).
Time To Live TLV Carries the TTL of device information
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