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Chapter 12: Link Layer Discovery Protocol
Link Layer Discovery Protocol (LLDP) is used to discover basic information about
neighboring devices on the local broadcast domain. LLDP is a Layer 2 protocol that
uses periodic broadcasts to advertise information about the sending device.
Advertised information is represented in Type Length Value (TLV) format according
to the IEEE 802.1ab standard, and can include details such as device identification,
capabilities and configuration settings. LLDP also defines how to store and maintain
information gathered about the neighboring network nodes it discovers. This
information can be used by SNMP applications to simplify troubleshooting, enhance
network management, and maintain an accurate network topology.
Setting Basic LLDP Timing Attributes
Use the LLDP Configuration screen to set attributes for general functions such as
globally enabling LLDP on the switch, setting the message ageout time, and setting
the frequency for broadcasting general advertisements or reports about changes in
the LLDP MIB.
Command Attributes
• LLDP – Enables LLDP globally on the switch. (Default: Disabled)
• Transmission Interval – Configures the periodic transmit interval for LLDP
advertisements. (Range: 5-32768 seconds; Default: 30 seconds)
This attribute must comply with the following rule:
(Transmission Interval * Hold Time Multiplier) ″ 65536, and
Transmission Interval >= (4 * Delay Interval)
• Hold Time Multiplier – Configures the time-to-live (TTL) value sent in LLDP
advertisements as shown in the formula below. (Range: 2-10; Default: 4)
The time-to-live tells the receiving LLDP agent how long to retain all information
pertaining to the sending LLDP agent if it does not transmit updates in a timely
manner.
TTL in seconds is based on the following rule:
(Transmission Interval * Holdtime Multiplier) ″ 65536.
Therefore, the default TTL is 4*30 = 120 seconds.
• Delay Interval – Configures a delay between the successive transmission of
advertisements initiated by a change in local LLDP MIB variables.
(Range: 1-8192 seconds; Default: 2 seconds)
The transmit delay is used to prevent a series of successive LLDP transmissions
during a short period of rapid changes in local LLDP MIB objects, and to increase
the probability that multiple, rather than single changes, are reported in each
transmission.
This attribute must comply with the rule: (4 * Delay Interval) ″ Transmission Interval
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