DebugPrivileged EXEC

debug ip dhcp server events

Use this command to monitor DHCP server events in real time, such as address assignments, renewals, and conflicts, for troubleshooting DHCP operation on a Cisco IOS router acting as a DHCP server.

Syntax·Privileged EXEC

debug ip dhcp server events

When to Use This Command

Troubleshooting why a client is not receiving an IP address from the DHCP server.
Monitoring DHCP address pool exhaustion or conflicts in a production network.
Verifying DHCP server behavior after configuration changes, such as new pools or exclusions.
Debugging DHCP relay agent interactions when the server is on a different subnet.

Command Examples

Basic DHCP server events debug

debug ip dhcp server events

DHCPD: DHCPDISCOVER received from 0050.7966.6800 on interface GigabitEthernet0/0
DHCPD: Sending DHCPOFFER to 192.168.1.10 (client 0050.7966.6800)
DHCPD: DHCPREQUEST received from 0050.7966.6800
DHCPD: Sending DHCPACK to 192.168.1.10 (client 0050.7966.6800)
DHCPD: DHCPINFORM received from 192.168.1.10
DHCPD: Sending DHCPACK to 192.168.1.10 (client 0050.7966.6800)
DHCPD: DHCPRELEASE received from 192.168.1.10
DHCPD: Released IP 192.168.1.10 for client 0050.7966.6800

Line 1: DHCPDISCOVER received from client MAC 0050.7966.6800 on G0/0. Line 2: Server offers IP 192.168.1.10 to that client. Line 3: Client requests the offered IP. Line 4: Server acknowledges and assigns the IP. Lines 5-6: Client sends DHCPINFORM (e.g., for renewal) and server acknowledges. Lines 7-8: Client releases the IP, server marks it as free.

Debug with address conflict detection

debug ip dhcp server events

DHCPD: DHCPDISCOVER received from 0011.2233.4455 on interface GigabitEthernet0/1
DHCPD: Ping test for address 192.168.2.10
DHCPD: Ping failed - address 192.168.2.10 is available
DHCPD: Sending DHCPOFFER to 192.168.2.10 (client 0011.2233.4455)
DHCPD: DHCPREQUEST received from 0011.2233.4455
DHCPD: Sending DHCPACK to 192.168.2.10 (client 0011.2233.4455)
DHCPD: DHCPDECLINE received from 0011.2233.4455 for address 192.168.2.10
DHCPD: Marking 192.168.2.10 as declined

Line 1: Client discovery. Line 2: Server pings the candidate address to check for conflicts. Line 3: Ping fails, so address is free. Lines 4-6: Normal offer/request/ack. Line 7: Client sends DHCPDECLINE indicating address conflict (e.g., duplicate IP detected via ARP). Line 8: Server marks the address as declined and will not reuse it until cleared.

Understanding the Output

The debug output shows each DHCP server event as it occurs. Key messages: DHCPDISCOVER (client searching), DHCPOFFER (server proposing an IP), DHCPREQUEST (client accepting or renewing), DHCPACK (server confirming assignment), DHCPNAK (server rejecting), DHCPDECLINE (client reporting conflict), DHCPRELEASE (client releasing IP), and DHCPINFORM (client requesting options). Each line includes the client MAC address and the IP address involved. Watch for DHCPNAK messages indicating server cannot fulfill request (e.g., pool exhausted, wrong subnet). DHCPDECLINE indicates duplicate IP detection. DHCPRELEASE shows clients voluntarily releasing addresses. In a healthy network, you should see a clean sequence of DISCOVER-OFFER-REQUEST-ACK. Frequent DHCPNAK or DECLINE events indicate configuration issues or IP conflicts.

CCNA Exam Tips

CCNA exam may ask which debug command to use to see DHCP server address assignments in real time.

Remember that debug ip dhcp server events shows the DORA process; debug ip dhcp server packets shows raw packet details.

Be aware that excessive debug can impact router performance; always use with caution and disable with undebug all.

The exam might test that DHCPDECLINE occurs when a client detects an IP address conflict via ARP.

Common Mistakes

Leaving debug enabled after troubleshooting, which can cause high CPU usage and log flooding.

Confusing debug ip dhcp server events with debug ip dhcp server packets; events shows summary, packets shows full packet contents.

Forgetting that the router must be configured as a DHCP server (ip dhcp pool) for this debug to produce output.

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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