Unable to get IP in Cisco network due to DHCP conflict

Equipment: Cisco 3750 core switch

Recently, clients in the private network are often unable to obtain IP automatically through DHCP, but there are not many IP in use online.

Show ip dhcp binding

Check that the address is not exhausted.

Show ip dhcp pool + pool name

Dozens of IP were eaten because the address does not match the setting.

Show ip dhcp conflict

It was found that all the eaten IP were occupied here.

Clear ip dhcp conflict *

Clear all conflicting IP

After checking the data, it turns out that when DHCP server detects that IP is occupied, it will record log, and dhcp server will no longer allocate the IP. Unless the device is rebooted or through clear ip dhcp conflict, the address pool will become smaller and smaller until it cannot be allocated. So the client cannot get the IP automatically and can only set the static IP.

You can cancel the logging of address conflicts through no ip dhcp conflict log.

Pool DHCPLIST:

Utilization mark (high/low): 100 / 0

Subnet size (first/next): 0 / 0

Total addresses: 254

Leased addresses: 11

Excluded addresses: 185

Pending event: none

1 subnet is currently in the pool:

Current index IP address range Leased/Excluded/Total

10.100.10.185 10.100.10.1-10.100.10.254 11 / 185 / 254