Hello guys a have a problem which i never faced until now.

I have a VMware ESXi 4.0 running as a Captive Portal solution for a hotel but since this morning users are reporting that they cannot connect anymore on wifi network. I have checked syslog and found this strange message:

2016 Oct 5 05:35:14 controller dhcpd: DHCPREQUEST for 172.27.32.2 from f4:5c:89:09:ea:c5 (KitchenardsiPad) via 172.27.32.1
2016 Oct 5 05:35:14 controller dhcpd: DHCPACK on 172.27.32.2 to f4:5c:89:09:ea:c5 (KitchenardsiPad) via 172.27.32.1
2016 Oct 5 05:35:14 controller dhcpd: 4 bad udp checksums in 6 packets


After every DHCPACK is bad udp checksums.

Please tell me what infos should I give you for help.

Best regards.

UDP is bad by design. It is connectionless. However that is not the checksum issue and may or may not be related to this connection issue. Let's start with checksum.
One site suggests this. "The simplest workaround is to change the virtual NIC type from virtio to Intel e1000 in KVM. Apparently this driver calculates checksums. But virtio is the default driver type." The virtual nic usually has a setting to offload the checksum and by most apps, the checksum will fail when the work is offloaded. Wireshark will reveal this also.

Try that first. I get the feeling however that you have other issues with how a device is allowed to connect. May be something like no more leases for some reason. May be that you need to use wireshark to see why the handshake is stopping or where it failed then act on that.

The real question is we have to ask that I assume this did work at one time. Then some change happened. Can we discover the change? What all could have changed? Could it be some update? Some failure of the software? Some hardware fail(not likely)? Or is it possible that some attack or data failure caused this?