JPNAS.NET / Cheat Sheets
📡 Networking
Commands for finding network problems on Windows and Linux, step by step from the IP address to the service – plus the address ranges and port numbers I look up most often.
Open in the interactive Cheat Sheets
My address
ipconfig /all | Windows: IP address, gateway, DNS servers and MAC address of every adapter. |
ip a ip route | Linux: addresses / routes, including the default gateway. |
ipconfig /release ipconfig /renew | Windows: give back the address and ask the DHCP server for a new one. |
nmcli device show | Linux with NetworkManager: everything about the connections. |
Is it reachable?
ping 192.168.1.1 | Does the router answer? |
ping 1.1.1.1 | Does the Internet answer – by IP address, without DNS? |
ping -c 4 jpnas.net | Linux: only 4 pings (otherwise it runs until Ctrl+C). |
tracert 1.1.1.1 traceroute 1.1.1.1 | Windows / Linux: every router on the way. |
mtr 1.1.1.1 pathping 1.1.1.1 | Linux / Windows: route and packet loss on every hop. |
DNS
nslookup jpnas.net | Which IP address does this name have? |
nslookup jpnas.net 1.1.1.1 | Ask a specific DNS server – to compare with your own. |
dig +short jpnas.net dig MX jpnas.net | Linux: only the address / the mail servers of a domain. |
ipconfig /flushdns | Windows: clear the DNS cache. |
resolvectl status resolvectl flush-caches | Linux with systemd: DNS settings / clear the cache. |
Ports and connections
Test-NetConnection jpnas.net -Port 443 | PowerShell: is this port reachable? |
nc -zv jpnas.net 443 | Linux: the same with netcat. |
ss -tulpn | Linux: which programs listen on which ports. |
netstat -ano | findstr LISTENING | Windows: listening ports with process IDs. |
curl -I https://jpnas.net/ | Ask a web server only for the headers – status code, server, redirects. |
Speed and Wi-Fi
iperf3 -s | Start an iperf3 server on one computer. |
iperf3 -c 192.168.1.10 | Measure the speed to it from another one (add -R for the other direction). |
netsh wlan show interfaces | Windows: Wi-Fi signal, channel, speed and band. |
nmcli dev wifi | Linux: Wi-Fi networks around you with signal and channel. |
Addresses to remember
10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 | Private address ranges – used at home and in companies, not on the Internet. |
169.254.x.x | The computer gave itself an address because no DHCP server answered. |
127.0.0.1 ::1 | Localhost – this computer itself (IPv4 / IPv6). |
/24 = 255.255.255.0 | A typical home network: 254 usable addresses. |
1.1.1.1 9.9.9.9 8.8.8.8 | Public DNS servers of Cloudflare, Quad9 and Google – good for testing. |
Ports to remember
22 | SSH |
53 | DNS |
80 443 | HTTP / HTTPS |
25 587 993 | Mail: server-to-server / sending from a mail program / IMAP |
3389 | Windows Remote Desktop – never open it to the Internet |
1883 8883 | MQTT / MQTT over TLS |
51820 | WireGuard (UDP) |