@kuba Are you using DHCP? Guess so, so that's DHCP Server config. If you aren't using DHCP it's configured manually.
Why? I can't see a reason for that in private networks.
How? Can be offered by DHCP or configured manually depending on how it's done on your system. netplan, network manager, manually. Some do it in /etc/network/interfaces others in /etc/sysconfig/network-scripts/