Invalid DHCP range. Start address is greater than end address.

[smecio]

After upgrading from FortiOS 7.4.4 to FortiOS 7.6.0 on Fortigate 100F I cannot modify an interface by GUI because of the following error message:

"Invalid DHCP range. Start address is greater than end address."

The interface IP address is 192.168.68.2/23 manual mode and DHCP range is 192.168.68.100-192.168.69.254 with subnet 255.255.254.0.

On the other hand, I can modify its configurations in CLI. Have no idea what's wrong here?

[akileshc · Accepted solution]

The issue you are facing is a known issue, documented under engineering ticket 1051961. The problem occurs when IP addresses cannot be assigned within a configured IP range due to a DHCP server issue. You can find more details about this in the release notes and this is expected to be fixed in next patch 7.6.1.

 https://docs.fortinet.com/document/fortigate/7.6.0/fortios-release-notes/236526/known-issues 

[smecio]

Thanks for your information. I wonder: Do clients have difficulties in acquiring valid IP addresses by DHCP because of the above known issue? We bought some UniFi Lite 16 PoE switches some of which fail to acquire IP addresses all the time so that they are absolute out of control.

[NoneEng]

Looks like so:

1051961 - On FortiGate, IP addresses cannot be assigned within a configured IP range due to a DHCP server issue.