What is Link Layer Discovery Protocol (LLDP)? | How does LLDP work? | How to configure LLDP?
What is Link Layer Discovery Protocol (LLDP)? | How link layer discovery protocol work? | LLDP default configuration? | how to configure LLDP?
Link Layer Discovery Protocol
LLDP it’s a nonproprietary protocol that works at layer 2. It is an open IEEE-standard 802.1AB. LLDP is an alternative to CDP. LLDP runs over the data link layer and it collects information about the neighboring devices. This information will help us in troubleshooting and documentation. LLDP and Cisco CDP work similarly but the big difference is that LLDP is a standard while CDP is a Cisco proprietary.
LLDP has similar capabilities to CDP and there is an enhanced version to specifically address the voice application this version is called LLDP-MED (media endpoint discovery) but LLDP and LLDP-MED are not compatible.
LLDP supports a defined set of attributes that contain a T-type, L-length, and V-value, these are called TLVs. It is used to discover neighbors’ devices. LLDP support devices use TLV to send and receive information and store the information in a local table.
How link layer discovery protocol work?
First, you must enable it on the devices because by default LLDP is disabled, and remember not all Cisco IOS routers support LLDP. LLDP-enabled devices send LLDP advertisements to LLDP neighbors and the information is stored in the MIB database locally. This information can be accessed using SNMP.
What information is stored?
Device name and description
Port name
IP management address
Capabilities
MAC address
MDI power
Link aggregation
VLAN
LLDP default configuration: -
IOU1(config)#lldp ?
holdtime Specify the holdtime (in sec) to be sent in packets
reinit Delay (in sec) for LLDP initialization on any interface
run Enable LLDP
timer Specify the rate at which LLDP packets are sent (in seconds)
tlv-select Selection of LLDP TLVs to send
LLDP is disabled by default
LLDP hold time – 120 seconds
LLDP reinitialization delay – 2 seconds
LLDP timer (packet update frequency) – 30 seconds
LLDP tlv-select – to send and receive all TLVs.
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