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B

Bandwidth measurement

Server (IP:192.168.0.2)

iperf3 -s

Client

# 4 parallel TCP streams, 30-second test, 1‑second reports
# iperf3 -c SERVER_IP -P 4 -t 30 -i 1, e.g.:
iperf3 -c 192.168.0.2 -P 4 -t 30 -i 1

Bridge networks

Setup: Two computers: M and S. M has two network cards but S only one. M's interface eno1 has access to the internet. S's interface eth0 is connected to M's second interface, enp1s0. The goal is to make S have access to the internet.

Execute at M

# Ensure forwarding
sudo sysctl -w net.ipv4.ip_forward=1


# Allow forwarding between interfaces (explicitly)
sudo iptables -A FORWARD -i enp1s0 -o eno1 -j ACCEPT
sudo iptables -A FORWARD -i eno1 -o enp1s0 -m state --state RELATED,ESTABLISHED -j ACCEPT

sudo iptables -t nat -A POSTROUTING -o eno1 -j MASQUERADE

Revert with

sudo sysctl -w net.ipv4.ip_forward=0
sudo iptables -F
sudo iptables -t nat -F

# or simply reboot

And to make changes persist

# Make IP forwarding permanent
echo 'net.ipv4.ip_forward=1' | sudo tee -a /etc/sysctl.conf

# Save iptables rules
sudo apt install iptables-persistent -y
sudo iptables-save | sudo tee /etc/iptables/rules.v4

D

Discover others in subnet

Say you sit at a pc with IP address 192.168.0.200 and you need to identify which devices it can reach in its subnet:

# Scan the entire subnet, i.e. look under 192.168.0.1--192.168.0.255
nmap -sn 192.168.0.0/24

F

File exchange (simple; for one-off type of situations)

Receiver (IP:192.168.0.2)

# netcat -l -p PORT > FILE, e.g.:
netcat -l -p 1234 > file_rx.txt

Transmitter

# nc RX_IP PORT -q 0 < file_tx.file
netcat 192.168.0.2 1234 -q 0 < file_tx.txt

or

# cat file.txt | netcat RX_IP PORT -q 0, e.g.:
cat file_tx.txt | netcat 192.168.0.2 1234 -q 0

File exchange (lightweight)

Either execute the second code fence directly or add it to your .bashrc. Then simply navigate to the directory in which the file(s) you want to send to another party reside and execute httphere there. You should see something like the following. Finally simply communicate to the other party the url http://169.4.4.14:10337: she should be seeing the contents of the directory.

> httphere
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    13  100    13    0     0     65      0 --:--:-- --:--:-- --:--:--    65
Serving HTTP on http://169.4.4.14:10337 from directory [/home/afilot]
Serving HTTP on http://169.4.4.14:10337 from directory [/home/afilot]
httphere()
{
    script="$(basename "$0")";
    function display_help ()
    {
        echo "$script - Quicky spin up a simple HTTP server for a directory.";
        echo "Usage: $script [arguments]";
        echo;
        echo "  -h/--help - Print help and exit.";
        echo "  -p/--port - Set the port number to bind to (defaults to 10337).";
        echo "  -d/--directory - Set the root directory to serve from (defaults to current).";
        exit 0
    };
    while [[ $# -gt 0 ]]; do
        case "$1" in
            -h | --help)
                display_help
            ;;
            -p | --port)
                port="$2";
                shift
            ;;
            -d | --directory)
                directory="$2";
                shift
            ;;
            *)
                echo "Unknown option: $1";
                display_help
            ;;
        esac;
        shift;
    done;
    port=${port:-10337};
    directory=${directory:-$(pwd)};
    if [[ $port -lt 1024 ]]; then
        echo "Warning: Ports below 1024 require root privileges.";
        echo "Please run this script with 'sudo' if you intend to use port $port.";
        exit 1;
    fi;
    ip=$(curl ifconfig.me/ip);
    echo "Serving HTTP on http://$ip:$port from directory [$directory]";
    python3 - <<EOF
import os
import time
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer

class CustomHTTPRequestHandler(SimpleHTTPRequestHandler):
    def list_directory(self, path):
        try:
            list = os.listdir(path)
        except OSError:
            self.send_error(404, "No permission to list directory")
            return None

        list.sort(key=lambda a: a.lower())

        def human_readable_size(size):
            for unit in ['bytes', 'KB', 'MB', 'GB', 'TB']:
                if size < 1024.0:
                    return f"{size:.2f} {unit}"
                size /= 1024.0
            return f"{size:.2f} PB"

        r = []
        r.append('<!DOCTYPE HTML>')
        r.append('<html><head>')
        r.append('<meta charset="utf-8">')
        r.append('<title>Directory listing for %s</title>' % self.path)
        r.append('<style>')
        r.append('table { width: 100%%; border-collapse: collapse; }')
        r.append('th, td { padding: 0px; text-align: left; }')
        r.append('th { background-color: #f4f4f4; }')
        r.append('</style>')
        r.append('</head><body>')
        r.append('<h1>Directory listing for %s</h1>' % self.path)
        r.append('<hr>')
        r.append('<table>')
        r.append('<tr><th>Name</th><th>Size</th><th>Last Modified</th></tr>')

        if self.path != '/':
            r.append('<tr><td><a href="..">Parent Directory</a></td><td></td><td></td></tr>')

        for name in list:
            fullname = os.path.join(path, name)
            displayname = name
            size = os.path.getsize(fullname)
            last_modified = time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(os.path.getmtime(fullname)))

            if os.path.isdir(fullname):
                displayname = name + "/"
                r.append('<tr><td><a href="%s">%s</a></td><td>DIR</td><td>%s</td></tr>' % (displayname, displayname, last_modified))
            else:
                readable_size = human_readable_size(size)
                r.append('<tr><td><a href="%s">%s</a></td><td>%s</td><td>%s</td></tr>' % (displayname, displayname, readable_size, last_modified))

        r.append('</table>')
        r.append('<hr>')
        r.append('</body></html>')
        encoded = '\n'.join(r).encode('utf-8', 'surrogateescape')

        self.send_response(200)
        self.send_header("Content-type", "text/html; charset=utf-8")
        self.send_header("Content-Length", str(len(encoded)))
        self.end_headers()
        self.wfile.write(encoded)
        return None

if __name__ == '__main__':
    server_address = ('0.0.0.0', $port)
    httpd = ThreadingHTTPServer(server_address, CustomHTTPRequestHandler)
    print(f"Serving HTTP on http://$ip:$port from directory [$directory]")
    httpd.serve_forever()
EOF
}

File exchange (heavyweight)

Use 9001/copyparty as a file server