show ip dhcp conflict
Displays IP address conflicts detected by the DHCP server, helping administrators identify and resolve duplicate IP assignments on the network.
show ip dhcp conflictWhen to Use This Command
- Troubleshooting duplicate IP address issues reported by users or network monitoring tools.
- Verifying that a DHCP server has not assigned an IP already in use after a network change or outage.
- Auditing DHCP scope health to ensure no conflicts exist before performing maintenance.
- Investigating rogue DHCP servers or misconfigured static IPs that cause address conflicts.
Command Examples
Viewing all DHCP conflicts
show ip dhcp conflictIP address Detection method Detection time VRF 192.168.1.33 Ping Mar 01 2025 10:15 AM default 192.168.1.45 Gratuitous ARP Mar 01 2025 10:22 AM default 10.0.0.12 Ping Feb 28 2025 03:45 PM default
Each row shows a conflicting IP address, how it was detected (Ping or Gratuitous ARP), the date and time of detection, and the VRF instance (usually 'default').
Clearing DHCP conflicts
clear ip dhcp conflict *This command clears all recorded DHCP conflicts from the router's memory. No output is displayed upon success.
Understanding the Output
The 'show ip dhcp conflict' output lists every IP address that the DHCP server has detected as conflicting. The 'Detection method' column indicates how the conflict was discovered: 'Ping' means the server sent an ICMP echo request and received a reply, suggesting the IP is already in use; 'Gratuitous ARP' means the server received an ARP reply for the IP before offering it. The 'Detection time' shows when the conflict was logged. The 'VRF' column indicates the Virtual Routing and Forwarding instance (typically 'default' for global routing). A healthy network should have no entries; any entry indicates a problem that needs investigation, such as a static IP overlapping with the DHCP pool or a rogue DHCP server.
CCNA Exam Tips
CCNA exam may ask which command displays DHCP conflicts; remember 'show ip dhcp conflict'.
Know that conflicts can be detected via Ping or Gratuitous ARP; the exam might test these detection methods.
Understand that clearing conflicts does not resolve the underlying issue; it only removes the log entry.
Be aware that the 'clear ip dhcp conflict *' command clears all conflicts; the asterisk is required.
Common Mistakes
Mistake: Forgetting to clear conflicts after resolving the duplicate IP; the conflict entry remains until cleared.
Mistake: Assuming 'show ip dhcp conflict' shows all DHCP issues; it only shows conflicts, not other problems like scope exhaustion.
Mistake: Using 'clear ip dhcp conflict' without the asterisk; the command requires an IP address or '*' to clear all.
Related Commands
show ip dhcp binding
Displays the current DHCP binding table, showing which IP addresses have been leased to clients, along with their MAC addresses, lease expiration, and type of binding.
show ip dhcp server statistics
Displays DHCP server statistics, including the number of messages sent and received, to monitor DHCP server performance and troubleshoot issues.
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