Show IP DHCP Conflict Command on CISCO Router/Switch


Show IP DHCP Conflict


This command shows information about IP conflicts that are detected during the DHCP negotiation. IP conflicts occur when hosts have statically assigned IP addresses that are within the DHCP configured range, but are not excluded.


Router#show ip dhcp conflict


Below is an example of show ip dhcp conflict. First, we will configure R2 to provide DHCP services.

R2(config)#ip dhcp pool VLAN
R2(dhcp-config)#network /24

Now we will change R2’s Fa0/0 IP address to be the first address in the range.

R2(config)#int fa0/0
R2(config-if)#ip add

We then configure R1’s Fa0/0 interface to receive its address via DHCP. Notice how R1 reaches as its address.

R1(config)#int fa0/0
R1(config-if)#ip add dhcp
R1(config-if)#no shut
*Mar 1 01:54:31.603: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor (FastEthernet0/0) is down: interface down
*Mar 1 01:54:41.947: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor (FastEthernet0/0) is up: new adjacency
*Mar 1 01:54:42.947: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0/0 assigned DHCP address, mask, hostname R1

*Mar 1 01:39:42.143: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor (FastEthernet0/0) is up: new adjacency

When we check R2, we can see that there was a conflict when R2 tried to offer as an address.

R2(config-if)#do show ip dhcp conflict
IP address Detection method Detection time VRF Gratuitous ARP Mar 01 2002 01:54 AM

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