Link Layer Discovery Protocol (LLDP)

22 Oct, 2021
LLDP stands for Link Layer Discovery Protocol. It is an open IEEE-standard (802.1AB) Layer 2 protocol. LLDP is the open-source alternative for CDP (Cisco Discovery Protocol) which is also a device discovery protocol that runs over Layer 2 (the data link layer) only on Cisco-manufactured devices (routers, bridges, access servers, and switches).
LLDP runs over the data link layer which allows two different devices to gather hardware and protocol information about neighboring devices that is useful in troubleshooting the network.
It supports a defined set of attributes that it uses to discover neighbor devices and are referred to as TLVs which are as follows:
T- type 
L- length
V- value descriptions
Devices running LLDP, on one of their interfaces, uses TLVs to receive and send information to their neighbors. These devices store the information of neighboring devices in a local table that can be accessed using SNMP (Simple Network Management Protocol). Information stored by the devices includes:
System name & description
Port name & description
IP management address
VLAN
Capabilities of the neighbor device
MAC address
MDI power
Link aggregation
Features of LLDP : LLDP enabled devices can 
Discover neighboring devices.
Advertise information about their layer-2 configurations to their neighbors.
Be troubleshot and fixed easily.
Use a level of Plug-and-Play configuration of peripheral devices.
Default LLDP configuration :
LLDP global state – Disabled
LLDP hold time – 120 seconds
LLDP timer (packet update frequency) – 30 seconds
LLDP reinitialization delay – 2 seconds
LLDP tlv-select – to send and receive all TLVs.
LLDP interface state – Enabled
LLDP receive – Enabled
LLDP transmit Enabled
LLDP med-tlv-select – to send all LLDP-MED TLVs
LLDP Packet Format :LLDP information is transmitted and/or received by neighbor devices via each of their LLDP enabled interfaces at a fixed interval of time in the form an Ethernet frame. Each Ethernet frame contains an LLDP data unit (LLDPDU). LLDPDU is a sequence of TLV structures. LLDP ethernet frame starts with the following compulsory TLVs :
Chassis ID
Port ID
Time to Live (TTL)
LLDP Packet Format
Applications of LLDP :
This protocol is used in data center bridging requirements.
It is used to advertise Power over Ethernet (PoE).
Advantages of LLDP :
It can run on cisco and non-cisco devices.
It is an open standard protocol recommended by CISCO too.
LLDP – MED extension gives an edge over CDP.
Disadvantages of LLDP :
On VMware switches the only protocol supported for discovery is CDP.
More cost of running LLDP over CDP.
LLDP Configuration :
Disabling and enabling LLDP globally 
# enabling LLDP

R1# configure terminal
R1(config)# lldp run
#disabling LLDP

R1# configure terminal
R1(config)# no lldp run
Disabling and Enabling LLDP protocol on an Interface 
#enabling LLDP on interface

R1# configure terminal
R1(config)# interface GigabitEthernet 1/1
R1(config-if)# lldp transmit
R1(config-if)# lldp receive
#disabling LLDP on interface

R1# configure terminal
R1(config)# interface GigabitEthernet 1/1
R1(config-if)# no lldp transmit
R1(config-if)# no lldp receive
Configuring a hold time, delay time, and  update frequency 
R1(config)# lldp holdtime 120
R1(config)# lldp reinit 5
R1(config)# lldp timer 15
Note: Use the “no” form of each of the above LLDP commands to return to the default setting on the device.
LLDP Router Configuration
Execute the same configuration for the R2 router to make it an LLDP neighbor of the R1 router in the above network.
To view the LLDP configuration on the router 
R1# show lldp 
LLDP command result
To view the detailed information about the LLDP neighbor devices 
R1# show lldp neighbors
LLDP neighbors command result
Picked
Computer Networks
Computer Networks
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.
Wireless Application Protocol
Mobile Internet Protocol (or Mobile IP)
GSM in Wireless Communication
Secure Socket Layer (SSL)
Introduction of Mobile Ad hoc Network (MANET)
Advanced Encryption Standard (AES)
Difference between MANET and VANET
Difference between FDMA, TDMA and CDMA
Dynamic Host Configuration Protocol (DHCP)
Cryptography and its Types