Link Layer Discovery Protocol (LLDP) is an industry-standard protocol (IEEE 802.1AB) implemented by various vendors. Unlike Cisco’s proprietary CDP, LLDP is typically disabled on Cisco devices by default and requires manual enabling. It’s possible for a device to run both CDP and LLDP simultaneously, although usually, only one is utilized.
LLDP messages are periodically sent to the multicast MAC address 0180.C200.000E. When a device receives an LLDP message, it processes and discards it, without forwarding it to other network devices. Therefore, only directly connected devices can become LLDP neighbors.
By default, LLDP messages are sent every 30 seconds, which is half the interval of CDP’s default 60 seconds. The default hold time for LLDP is 120 seconds. LLDP also features an additional timer known as the reinitialization delay, which delays the actual initialization of LLDP by 2 seconds.
To use LLDP on a network, you need to enable it both globally and on the interfaces of the Cisco devices you want it to work on.
How to Enable LLDP on Cisco Devices
LLDP is globally disabled by default and disabled on each interface of Cisco devices as well. To enable LLDP, you must first enable it globally and then on each interface of the Cisco device.
To enable LLDP globally, enter “lldp run” from global configuration mode.
R1(config)#lldp runTo enable LLDP transmission (tx) on a specific interface, use “lldp transmit” on the interface. This command prompts the interface to start sending LLDP messages. However, it won’t receive LLDP messages; it simply discards them.
To enable LLDP reception (rx), use “lldp receive” on the interfaces.
R1(config-if-range)#lldp transmit
R1(config-if-range)#lldp receiveRemember to enable both LLDP send and receive unless you have a reason to have an interface only send LLDP messages or vice versa.
How to Disable LLDP on Cisco Devices
To disable LLDP globally on the device, enter “no lldp run” from global configuration mode.
R1(config)#no lldp runTo disable LLDP Transmission (tx) on Specific Interfaces, enter “no lldp transmit” from the interface configuration mode.
To disable LLDP Reception (rx) on Specific Interfaces, enter “no lldp receive” from the interface configuration mode.
R1(config-if-range)#no lldp transmit
R1(config-if-range)#no lldp receiveHow to Configure LLDP Timers
The timer used to send messages is configured with “lldp timer <seconds>” commands.
R1(config)# lldp timer The LLDP holdtime is configured with “lldp holdtime <seconds>.”
R1(config)# lldp holdtime Finally, to configure the LLDP reinit timer, use “lldp reinit <seconds>,”
R1(config)# lldp reinit Where <seconds> is the time in seconds that you want to assign to the timer.
Network Topology
The network topology we will be making use of in this post is shown below. As you can see, it consist of 3 routers. In this demonstration, we will be enabling and disabling LLDP on the routers and then using the appropriate show command to view the LLDP-neighbor relationship.
LLDP Configuration on cisco devices
1. Enabling LLDP globally on the R1
R1(config)#lldp run
R1#show lldp
Global LLDP Information:
Status: ACTIVE
LLDP advertisements are sent every 30 seconds
LLDP hold time advertised is 120 seconds
LLDP interface reinitialisation delay is 2 seconds2. Enabling LLDP On interface of Cisco Devices.
Router1
R1(config)#interface range ethernet0/0-1
R1(config-if-range)#no shutdown
R1(config-if-range)#lldp transmit
R1(config-if-range)#lldp receive
R1(config-if-range)#exitRouter2
R2(config)#lldp run
R2(config)#interface ethernet0/0
R2(config-if)#no shutdown
R2(config-if)#lldp transmit
R2(config-if)#lldp receive
R2(config-if)#exitRouter3
R3(config)#lldp run
R3(config)#interface ethernet0/0
R3(config-if)#no shutdown
R3(config-if)#lldp transmit
R3(config-if)#lldp receive
R3(config-if)#exitLLDP Show Commands and Output
1. show lldp neighbors
This is used to check the list of LLDP neighbors on a Cisco device
R1#show lldp neighbors
Capability codes:
(R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device
(W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other
Device ID Local Intf Hold-time Capability Port ID
R3 Et0/1 120 R Et0/0
R2 Et0/0 120 R Et0/0
Total entries displayed: 22. show lldp neighbors detail
This show command display more details about LLDP neighbors
R1#show lldp neighbors detail
------------------------------------------------
Local Intf: Et0/1
Chassis id: aabb.cc00.3a00
Port id: Et0/0
Port Description: Ethernet0/0
System Name: R3
System Description:
Cisco IOS Software, Linux Software (I86BI_LINUX-ADVENTERPRISEK9-M), Version 15.7(3)M2, DEVELOPMENT TEST SOFTWARE
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2018 by Cisco Systems, Inc.
Compiled Wed 28-Mar-18 11:18 by prod_rel_te
Time remaining: 90 seconds
System Capabilities: B,R
Enabled Capabilities: R
Management Addresses - not advertised
Auto Negotiation - not supported
Physical media capabilities - not advertised
Media Attachment Unit type - not advertised
Vlan ID: - not advertised
------------------------------------------------
Local Intf: Et0/0
Chassis id: aabb.cc00.2a00
Port id: Et0/0
Port Description: Ethernet0/0
System Name: R2
System Description:
Cisco IOS Software, Linux Software (I86BI_LINUX-ADVENTERPRISEK9-M), Version 15.7(3)M2, DEVELOPMENT TEST SOFTWARE
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2018 by Cisco Systems, Inc.
Compiled Wed 28-Mar-18 11:18 by prod_rel_te
Time remaining: 98 seconds
System Capabilities: B,R
Enabled Capabilities: R
Management Addresses - not advertised
Auto Negotiation - not supported
Physical media capabilities - not advertised
Media Attachment Unit type - not advertised
Vlan ID: - not advertised
Total entries displayed: 23. show lldp interface
This show command check LLDP on all interfaces
R1#show lldp interface
Ethernet0/0:
Tx: enabled
Rx: enabled
Tx state: IDLE
Rx state: WAIT FOR FRAME
Ethernet0/1:
Tx: enabled
Rx: enabled
Tx state: IDLE
Rx state: WAIT FOR FRAME
Ethernet0/2:
Tx: enabled
Rx: enabled
Tx state: INIT
Rx state: WAIT PORT OPER
Ethernet0/3:
Tx: enabled
Rx: enabled
Tx state: INIT
Rx state: WAIT PORT OPER4.show lldp interface <interface_ID>
This commands Check LLDP on a specific interface.
R1#show lldp interface ethernet0/0
Ethernet0/0:
Tx: enabled
Rx: enabled
Tx state: IDLE
Rx state: WAIT FOR FRAMERelated Content
How to Configure And Verify CDP in Cisco Devices
I am a passionate Networking Associate specializing in Telecommunications.
With a degree in Electronic engineering, I possess a strong understanding of electronic systems and the intricacies of telecommunications networks. I gained practical experience and valuable insights working for a prominent telecommunications company.
Additionally, I hold certifications in networking, which have solidified my expertise in network architecture, protocols, and optimization.
Through my writing skills, I aim to provide accurate and valuable knowledge in the networking field.
Connect with me on social media using the links below for more insights.
You can contact me using [email protected] or connect with me using any of the social media account linked below