Yesterday (early August 2021) my Ubuntu 20.04 installation started configuring all network interfaces (wifi, ethernet) with IPv4 addresses from the wrong network segment block, namely 192.168.0.x. IPv6 still worked fine.
I didn’t figure out whether that’s due to a change in the router or the OS (I suspect the router, because the situation improved when increasing the DHCP lease time [2]), this solution however [1] works for me.
The file
/etc/netplan/01-network-manager-all.yam
must be reconfigured, in my case
network:
renderer: networkd
version: 2
ethernets:
enp5s0:
dhcp4: true
dhcp-identifier: mac
wlp6s0:
dhcp4: true
dhcp-identifier: mac[1] networking – Wrong IP address from DHCP client on Ubuntu 18.04
https://superuser.com/questions/1338510/wrong-ip-address-from-dhcp-client-on-ubuntu-18-04
[2] What is a good DHCP lease time?
https://serverfault.com/questions/251815/what-is-a-good-dhcp-lease-timeout-configuration
George's Techblog 