show cdp neighbors detail
Displays detailed information about directly connected Cisco devices discovered via CDP, including IP addresses, IOS version, platform, and interface details, useful for verifying neighbor relationships and troubleshooting Layer 2 connectivity.
show cdp neighbors detailWhen to Use This Command
- Verify that a newly connected switch or router is properly linked and exchanging CDP information.
- Identify the IP address and IOS version of a neighboring device to determine compatibility or plan upgrades.
- Troubleshoot a missing route by checking if the expected neighbor is reachable via CDP.
- Document the network topology by collecting detailed neighbor information from multiple devices.
Command Examples
Basic CDP neighbor detail output
show cdp neighbors detail------------------------- Device ID: R2 Entry address(es): IP address: 192.168.1.2 Platform: Cisco 7206VXR, Capabilities: Router Interface: GigabitEthernet0/0, Port ID (outgoing port): GigabitEthernet0/1 Holdtime : 135 sec Version : Cisco IOS Software, 7200 Software (C7200-ADVENTERPRISEK9-M), Version 15.2(4)M6, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2015 by Cisco Systems, Inc. Compiled Mon 02-Mar-15 00:00 by prod_rel_team advertisement version: 2 VTP Management Domain: '' Duplex: full Power drawn: 0.00 Watts ------------------------- Device ID: SW1 Entry address(es): IP address: 10.0.0.2 Platform: cisco WS-C2960-24TT-L, Capabilities: Switch IGMP Interface: GigabitEthernet0/1, Port ID (outgoing port): FastEthernet0/24 Holdtime : 150 sec Version : Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version 15.0(2)SE, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2012 by Cisco Systems, Inc. Compiled Mon 18-Jun-12 00:00 by prod_rel_team advertisement version: 2 VTP Management Domain: '' Duplex: full Power drawn: 0.00 Watts
Device ID: Hostname of the neighbor. Entry address(es): IP address(es) of the neighbor (usually the management IP). Platform: Hardware model. Capabilities: Device type (Router, Switch, IGMP, etc.). Interface: Local interface on this device connecting to the neighbor. Port ID: Neighbor's interface connected to us. Holdtime: Remaining seconds before CDP entry expires. Version: Detailed IOS version string. advertisement version: CDP version (2 is common). VTP Management Domain: VTP domain (blank if not configured). Duplex: Negotiated duplex mode. Power drawn: PoE power consumption (0 if not PoE).
Filtering output for a specific interface
show cdp neighbors detail gigabitethernet 0/0------------------------- Device ID: R2 Entry address(es): IP address: 192.168.1.2 Platform: Cisco 7206VXR, Capabilities: Router Interface: GigabitEthernet0/0, Port ID (outgoing port): GigabitEthernet0/1 Holdtime : 135 sec Version : Cisco IOS Software, 7200 Software (C7200-ADVENTERPRISEK9-M), Version 15.2(4)M6, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2015 by Cisco Systems, Inc. Compiled Mon 02-Mar-15 00:00 by prod_rel_team advertisement version: 2 VTP Management Domain: '' Duplex: full Power drawn: 0.00 Watts
This variant shows only CDP neighbors reachable via GigabitEthernet0/0. Useful when troubleshooting a specific link. The output is identical in format but limited to that interface.
Understanding the Output
The output lists each neighbor separated by dashed lines. 'Device ID' is the hostname of the neighbor. 'Entry address(es)' shows the IP address(es) the neighbor advertises; this is critical for management and routing. 'Platform' indicates hardware model, useful for capacity planning. 'Capabilities' tells you if the device is a router, switch, or other (e.g., 'Switch IGMP' means a switch with IGMP snooping). 'Interface' is the local interface connecting to the neighbor, and 'Port ID' is the neighbor's interface. 'Holdtime' counts down from 180 seconds; if it reaches 0, the neighbor is considered lost. 'Version' provides the exact IOS version, helpful for compatibility checks. 'Duplex' should be 'full' for modern links; 'half' may indicate a duplex mismatch. 'Power drawn' is relevant for PoE devices. In a real network, you would use this to verify that all expected neighbors appear, check IP addresses for consistency with your documentation, and ensure IOS versions are compatible. Missing neighbors or incorrect IPs indicate configuration or connectivity issues.
CCNA Exam Tips
Remember that CDP is Cisco proprietary and enabled by default; the exam may ask about its Layer 2 nature.
Know that 'show cdp neighbors detail' provides IP addresses, which 'show cdp neighbors' does not.
Be aware that CDP version 2 is the default; version 1 is rarely used but may appear in legacy scenarios.
The holdtime is typically 180 seconds; if you see a lower value, the neighbor may be flapping.
Common Mistakes
Confusing 'show cdp neighbors' with 'show cdp neighbors detail' — the latter gives IP addresses and IOS version.
Assuming CDP works across routers without IP connectivity; CDP is Layer 2 and does not require IP.
Forgetting that CDP is disabled on some interfaces by default (e.g., on certain IOS versions or security configurations).
Misinterpreting 'Holdtime' as the time since last update; it is the remaining time before expiration.
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