= Connect two computers directly without a router with an Ethernet cable
For <IP (protocol)>-level communication, https://askubuntu.com/questions/22835/how-to-network-two-ubuntu-computers-using-ethernet-without-a-router/116680\#116680 just worked between <ciro santilli s hardware/P51> and <ciro santilli s hardware/P14s> both on <Ubuntu 23.10> connected with a regular <Cat 5e> cable.
On both machines, first we found the <Ethernet cable> interface name with the <ip CLI tool>:
``
ip a
``
which outputs on the P41s:
``
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp1s0f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether fc:5c:ee:24:fb:b4 brd ff:ff:ff:ff:ff:ff
3: wlp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 04:7b:cb:cc:1b:10 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.123/24 brd 192.168.1.255 scope global dynamic noprefixroute wlp2s0
valid_lft 61284sec preferred_lft 61284sec
inet6 fe80::3597:15d8:74ff:e112/64 scope link noprefixroute
valid_lft forever preferred_lft forever
``
so the interface was `enp1s0f0`, because `wlp` is wireless and `lo` is localhost.
So on the P14s we assign an IP of 10.0.0.10 to the P51:
``
sudo ip address add 10.0.0.10/24 dev enp1s0f0
``
Then on the P51 analogously, giving IP of 10.0.0.20 to the P14s:
``
sudo ip address add 10.0.0.20/24 dev enp0s31f6
``
And after that, P14s can:
``
ping 10.0.0.10
``
and P51 can:
``
ping 10.0.0.20
``
TODO after a few seconds, the settings appear to be forgotten, and `ping` stops working unless you do `sudo ip address add` on the local machine again. This seems to happen after a popup appears saying "Activation of network connection failed" as it fails to obtain Internet from the cable.
TODO list and delete such manual assignments we've made.