CDP / LLDPEXEC

show lldp neighbors detail

Displays detailed information about LLDP neighbors discovered on the switch.

Overview

The 'show lldp neighbors detail' command is a fundamental diagnostic tool on Cisco NX-OS (Nexus) switches for inspecting the Link Layer Discovery Protocol (LLDP) neighbor database. LLDP is an IEEE 802.1AB standard that allows network devices to advertise their identity, capabilities, and management addresses to directly connected neighbors. On Nexus switches, LLDP is enabled globally by default on all interfaces, though it can be disabled per interface or globally. This command provides a verbose view of each neighbor, including chassis ID (typically the MAC address), port ID, system name, system description, hold time, remaining time, capabilities, and management IP addresses. It is essential for verifying physical connectivity, discovering network topology, and troubleshooting Layer 2 issues. Network engineers use this command to confirm that expected neighbors are present, to check for unauthorized devices, and to ensure that management IPs are correctly advertised. In troubleshooting workflows, it helps isolate problems such as misconfigured interfaces, incompatible LLDP versions, or faulty cables. The command can be filtered by interface to focus on a specific link, making it efficient for targeted analysis. Understanding the output is crucial for maintaining a healthy network and for passing Cisco certification exams like CCNP.

Syntax·EXEC

show lldp neighbors detail [interface <interface>]

When to Use This Command

Verify LLDP neighbor details for a specific interface to confirm connectivity and device identity.
Troubleshoot missing or incomplete LLDP neighbor information on a trunk link.
Audit network topology by collecting detailed neighbor data from all interfaces.
Check management IP addresses of neighboring devices for remote access.

Parameters

Parameter	Syntax	Required	Description
interface	interface <interface>	Optional	Specifies a particular interface (e.g., ethernet 1/1) to display LLDP neighbor details for that interface only. If omitted, details for all interfaces are shown.

Command Examples

Show LLDP neighbors detail for all interfaces

show lldp neighbors detail

Local Intf: Ethernet1/1
  Chassis id: 0c75.bd3a.1234
  Port id: Ethernet1/1
  Local Port id: Ethernet1/1
  System Name: N9K-1
  System Description: Cisco Nexus 9000v, Version 9.3(10)
  Time remaining: 120 seconds
  Hold Time: 120 seconds
  Capabilities: Router, Bridge
  Management Addresses:
    IPv4: 192.168.1.1
  Interface Description: to N9K-2

Local Intf: Ethernet1/2
  Chassis id: 0c75.bd3a.5678
  Port id: Ethernet1/2
  Local Port id: Ethernet1/2
  System Name: N9K-2
  System Description: Cisco Nexus 9000v, Version 9.3(10)
  Time remaining: 100 seconds
  Hold Time: 120 seconds
  Capabilities: Router, Bridge
  Management Addresses:
    IPv4: 192.168.1.2
  Interface Description: to N9K-1

Shows two LLDP neighbors. Each entry includes local interface, chassis ID (MAC), port ID, system name, description, hold time remaining, capabilities, management IP, and interface description.

Show LLDP neighbors detail for a specific interface

show lldp neighbors detail interface ethernet 1/1

Local Intf: Ethernet1/1
  Chassis id: 0c75.bd3a.1234
  Port id: Ethernet1/1
  Local Port id: Ethernet1/1
  System Name: N9K-1
  System Description: Cisco Nexus 9000v, Version 9.3(10)
  Time remaining: 120 seconds
  Hold Time: 120 seconds
  Capabilities: Router, Bridge
  Management Addresses:
    IPv4: 192.168.1.1
  Interface Description: to N9K-2

Filters output to only show neighbor details for Ethernet1/1. Useful for targeted troubleshooting.

Understanding the Output

The output is organized per local interface. Each neighbor entry begins with 'Local Intf:' followed by the interface name. Key fields include: - Chassis id: The MAC address of the neighbor device. - Port id: The interface on the neighbor device. - Local Port id: The local interface (usually same as Local Intf). - System Name: Hostname of the neighbor. - System Description: Model and software version. - Time remaining: Seconds before the LLDP entry expires (should be less than Hold Time). - Hold Time: Maximum time the entry is kept without refresh (typically 120 seconds). - Capabilities: Advertised capabilities (e.g., Router, Bridge, Switch). - Management Addresses: IP addresses used for management (IPv4/IPv6). - Interface Description: Description configured on the neighbor's interface. Healthy values: Time remaining should be a positive number decreasing from Hold Time; if it reaches 0, the neighbor is unreachable. Management addresses should be reachable. Capabilities should match expected device role. Missing or 'N/A' fields may indicate misconfiguration or incompatible LLDP implementations.

Configuration Scenarios

Verifying LLDP Neighbor on a Trunk Link

Two Nexus switches are connected via a trunk link. You need to confirm LLDP is working and verify the neighbor's management IP.

Topology

[N9K-1] --- Ethernet1/1 --- [N9K-2]

Steps

1.On N9K-1, enter privileged EXEC mode.
2.Run 'show lldp neighbors detail interface ethernet 1/1'.
3.Check that the output shows N9K-2 with correct management IP.

Configuration

! No additional configuration needed if LLDP is enabled by default.
! To enable LLDP globally if disabled:
! lldp enable

Verify: Verify that the 'System Name' matches the hostname of N9K-2 and the 'Management Addresses' shows the expected IP (e.g., 192.168.1.2).

Watch out: If the neighbor is not displayed, ensure LLDP is enabled on both sides and the interface is not in a shutdown state.

Troubleshooting with This Command

When troubleshooting LLDP neighbor issues on Cisco NX-OS (Nexus), start by checking if LLDP is enabled globally with 'show lldp' and per interface with 'show lldp interface'. If a neighbor is missing, verify physical connectivity (cable, link lights) and that the interface is up/up. Use 'show lldp neighbors detail' to see if any neighbor is present; if not, check for LLDP packet drops with 'show lldp traffic'. Common issues include LLDP being disabled globally or on the interface, incompatible LLDP versions, or firewall rules blocking LLDP multicast (01:80:c2:00:00:0e). On Nexus, LLDP uses the standard TLV set; ensure the neighbor supports LLDP. If the neighbor appears but with incomplete information (e.g., no management address), the neighbor may not be configured to advertise it. Also, check the 'Time remaining' field: if it consistently drops to 0 and then resets, the neighbor is sending LLDP packets intermittently, possibly due to CPU overload or flapping interface. For persistent issues, enable LLDP debugging with 'debug lldp packets' (use with caution in production). Finally, compare with CDP output if both are enabled; CDP and LLDP may show different information.

CCNA Exam Tips

Remember that LLDP is a vendor-neutral protocol; Cisco also uses CDP. Know the differences for CCNP.

The 'Time remaining' field is critical for troubleshooting: if it consistently drops to 0, the neighbor is not sending LLDP updates.

Management addresses are used for network management; ensure they are correct for remote access.

Common Mistakes

Confusing LLDP with CDP; LLDP is IEEE 802.1AB, CDP is Cisco proprietary.

Assuming 'show lldp neighbors detail' shows all neighbors; it only shows neighbors that have sent LLDP packets.

Ignoring the 'Time remaining' field; a low value indicates a flapping or unreachable neighbor.

Platform Notes

On Cisco NX-OS (Nexus), LLDP is enabled by default on all interfaces, unlike Cisco IOS where it may be disabled. The command syntax is similar to IOS, but Nexus uses 'show lldp neighbors detail' without the 'lldp' prefix. On IOS, the equivalent command is 'show lldp neighbors detail'. Nexus also supports 'show lldp neighbors' for a summary view. For CDP, use 'show cdp neighbors detail'. On other platforms like Juniper JunOS, the equivalent is 'show lldp neighbors detail' or 'show lldp neighbor <interface> detail'. Arista EOS uses 'show lldp neighbors detail'. Note that Nexus switches support both LLDP and CDP simultaneously. In NX-OS versions prior to 9.3, LLDP might have been disabled by default; always verify with 'show lldp'.

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