I am using an ethernet shield on an arduino UNO and it went from connecting fine to getting a DHCP failed message at start up. Not aware of any changes that I made to anything between working and not working.
Currently troubleshooting with blynk Arduino_Ethernet example with baud rate changed to 115200
Check the range of IP addresses that your DHCP server is allowed to allocate. If it’s quite narrow then there may not be any available actresses left. Previously there may have been a spare that has then been used by another device such as a phone that’s joined the network.
If that’s not the issue then do all the usual stuff, reboot the router and any network switches, plug the Arduino direct into the router, disconnect as many other devices that you can, etc, etc.
Also, check that you only have one DHCP server on your network.
Pete.
