Shell: ping, nslookup, port, traceroute, ifconfig and arp (#90)

Network troubleshooting from the device itself, in the Shell and over both
consoles. ping, nslookup, port and traceroute each run on a task of their
own and print as they go, to the console that asked; one at a time, and
`cancel` stops it. ifconfig and arp answer at once: the interfaces (Wi-Fi
and the VPN), which is the default route, the DNS servers, the neighbours.

nslookup asks a DNS server itself, so it can say which server answered and
in how long, and ask another. A sized ping finds what a tunnel really
carries.

With a how-to, "When the network doesn't work", and the rest of the docs.
tls, ntp and netstat from the issue's list are not in this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

site/content/guide/shell.md

@@ -43,6 +43,21 @@ Type an App's name **with a capital letter** to open it, without going back to t
 
 The capital is the difference: every command is in small letters, every App starts with a capital. <kbd>Tab</kbd> completes them too.
 
+## The network
+
+For the day the network doesn't do what it should. Each of the first four takes a moment and prints as it goes; one runs at a time, and `cancel` stops it.
+
+| Command | Tells you |
+|---|---|
+| `ping 10.9.0.1` | Whether a host answers, and how fast. A count and a size may follow: `ping 10.9.0.1 10 1392` |
+| `nslookup roro9stack.net` | A name's addresses, which DNS server answered and in how long. Another server may follow: `nslookup roro9stack.net 9.9.9.9` |
+| `port git.twis.la 443` | Whether a TCP port is **open**, **refused** (the host is there, nothing listens) or silent (down, or filtered) |
+| `traceroute 9.9.9.9` | The routers on the way, one a line |
+| `ifconfig` | The interfaces (Wi-Fi, and the [VPN](/guide/vpn/) when it is up), their addresses, **which one is the default route**, and the DNS servers |
+| `arp` | The neighbours heard on the Wi-Fi: is the gateway there at all |
+
+A host can be a name or an address. [When the network doesn't work](/howto/network-check/) puts them in order.
+
 ## Deleting
 
 `rm` works as it does on Unix, with one addition: it asks.

site/content/guide/vpn.md

@@ -60,6 +60,8 @@ vpn auto on|off     start with Wi-Fi
 
 `vpn up` with a number of seconds is for trying a new configuration from a distance: if it cuts you off, it comes back by itself.
 
+To see it work: `ifconfig` shows the tunnel and whether it is the default route, and `ping`, `nslookup`, `port` and `traceroute` go the way real traffic goes. See [When the network doesn't work](/howto/network-check/).
+
 ## Limits
 
 One tunnel, to one server. IPv4 only: IPv6 addresses in the file are left out. The server can be an address or a name.