QTECH
Software Configuration Manual
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Chapter 19
LLDP configuration
19.1 Brief introduction of LLDP protocol
LLDP(Link Layer Discovery Protocol)is the new protocol defined by IEEE 802.1AB. It realizes proclaiming
information about itself to other neighbor devices through network and receives the bulletin information from
neighbor devices and stores it to standard MIB of LLDP. It is convenient for user to check the device model and
linked interfaces of downlink neighbor devices and maintains central office and manage network. Network
administrator can know the link of network layer 2 by accessing MIB.
19.1.1
LLDP Overview
Link Layer Discovery Protocol (LLDP) operates on data link layer. It stores and maintains the information
about the local device and the devices directly connected to it for network administrators to manage networks through
NMS (network management systems). In LLDP, device information is encapsulated in LLDPDUs in the form of TLV
(meaning type, length, and value) triplets and is exchanged between directly connected devices. Information in
LLDPDUs received is restored in standard MIB (management information base).
19.1.1.1
LLDP operating mode
LLDP can operate in one of the following modes.
·
TxRx mode. A port in this mode sends and receives LLDPDUs.
·
Tx mode. A port in this mode only sends LLDPDUs.
·
Rx mode. A port in this mode only receives LLDPDUs.
·
Disable mode. A port in this mode does not send or receive LLDPDUs.
LLDP is initialized when an LLDP-enabled port changes to operate in another LLDP operating mode. To
prevent LLDP from being initialized too frequently, LLDP undergoes a period before being initialized on an
LLDP-enabled port when the port changes to operate in another LLDP operating mode. The period is known as
initialization delay, which is determined by the re-initialization delay timer.
19.1.1.2
Sending LLDPDUs
A 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.)
19.1.1.3
Receiving LLDPDUs
An LLDP-enabled device operating in the TxRx mode or Rx mode validates the TLVs carried in the
LLDPDUs it receives and stores 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.
