Interfaces, addresses and subnets

Now you can fix the client's address so that the server becomes its neighbour.

Two commands change an interface's addresses. The address is written together with its prefix:

ip address del ADDRESS/PREFIX dev INTERFACE   # remove an address
ip address add ADDRESS/PREFIX dev INTERFACE   # add an address

add puts an address next to the ones already assigned: the old one stays until del removes it. Changes made with ip last until the network restarts; the lesson on Netplan shows how to keep them for good.