Track 4 · Lesson 1 of 5
Networking basics
Inspect your network with ifconfig, ip, ping and nmap, fetch pages with curl and wget, and connect over ssh from Termux.
Your phone is a networked computer. Termux gives you the same tools an administrator uses on a server. In this lesson you will find your own address, and test whether another host is reachable. You will fetch a page from the command line. You will also open a secure shell to another machine. You will also see how to read a service banner. And you will see why you must never scan a network you do not control.
What you'll be able to do
- Find your own IP address with
ifconfigandip addr. - Test reachability and round-trip time with
ping. - Run a basic
nmapscan and read the ports and versions it reports. - Fetch a page with
curl, read its headers with-I, and save it with-o. - Download a file with
wget. - Connect over
ssh. Understand the host-key fingerprint prompt.
Step 1: Install the tools
Termux does not include these commands by default. Install them in one call. The openssh package provides ssh and sshd. iproute2 provides ip, and net-tools provides ifconfig and netstat.
pkg install iproute2 net-tools nmap curl wget opensshReading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following NEW packages will be installed:
curl iproute2 net-tools nmap openssh wget
0 upgraded, 6 newly installed, 0 to remove and 0 not upgraded.
Setting up curl (8.8.0) ...
Setting up iproute2 (6.10.0) ...
Setting up nmap (7.95) ...
Setting up openssh (9.8p1) ...
Setting up wget (1.24.5) ...Step 2: Find your own address
ifconfig lists every network interface on the device. The lo interface is the loopback, which only talks to itself. The interface that faces the network is usually wlan0 on a phone.
ifconfiglo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.42 netmask 255.255.255.0 broadcast 192.168.1.255
ether 02:00:00:00:00:00 txqueuelen 1000 (Ethernet)The inet line under wlan0 is your address on the local network. Here it is 192.168.1.42. Addresses that begin with 192.168, 10. or 172.16 through 172.31 are private. They are only reachable inside your own network.
The ip command shows the same information in a modern layout.
ip addr1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
2: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP
link/ether 02:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.42/24 brd 192.168.1.255 scope global wlan0The /24 after the address is the prefix length. It is another way of writing the netmask 255.255.255.0.
Step 3: Test reachability with ping
ping sends a small packet and waits for a reply. Use -c to set how many packets to send. Otherwise it runs until you stop it.
ping -c 3 192.168.1.1PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=3.21 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=2.88 ms
64 bytes from 192.168.1.1: icmp_seq=3 ttl=64 time=3.05 ms
--- 192.168.1.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 2.880/3.047/3.210/0.135 msThe address 192.168.1.1 is usually your router. A reply with 0% packet loss means the host is reachable. The time value is the round trip in milliseconds, and the summary line gives the average.
Step 4: Scan ports with nmap
nmap checks which ports on a host are open. The -p flag names the ports to check. -sV asks nmap to identify the service and its version.
Only run nmap against systems you own or have written permission to test. Scanning a network you do not control can break its terms of service, and in many countries it is a criminal offence. Your own router and your own devices are fine.
nmap -sV -p 22,80,8022 192.168.1.10Starting Nmap 7.95 ( https://nmap.org ) at 2026-01-26 12:00 IST
Nmap scan report for 192.168.1.10
Host is up (0.0040s latency).
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 9.6 (protocol 2.0)
80/tcp open http nginx 1.24.0
8022/tcp closed unknown
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 6.21 secondsEach line names a port, and says whether it is open or closed. It gives the service, and the version when -sV could work it out. An open port is a service accepting connections. Each one is something to keep patched.
Step 5: Fetch a page with curl
curl makes an HTTP request and prints the response body. With no options it does a plain GET and writes the page to the screen.
curl http://example.com<!doctype html>
<html>
<head>
<title>Example Domain</title>
</head>
<body>
<h1>Example Domain</h1>
</body>
</html>Add -I to ask for the headers only. This is the quickest way to check whether a page exists and what type it is.
curl -I http://example.comHTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Content-Length: 1256
Connection: keep-aliveThe first line holds the status code. 200 means success, 404 means not found, 301 or 302 means a redirect.
To save the response instead of printing it, use -o followed by a filename.
curl -o page.html http://example.com % Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1256 100 1256 0 0 8423 0 --:--:-- --:--:-- --:--:-- 8423The progress line shows how much was transferred. Confirm the file is on disk.
ls -l page.html-rw-r--r-- 1 u0_a123 u0_a123 1256 Jan 26 12:00 page.htmlStep 6: Download with wget
wget is built for downloading. Give it a URL and it saves the file under its own name. It follows redirects on its own.
wget http://example.comHTTP request sent, awaiting response... 200 OK
Length: 1256 (1.2K) [text/html]
Saving to: index.html
index.html saved [1256/1256]The last line confirms the filename and the number of bytes saved. Because the URL pointed at a directory-style path, wget used the default name index.html.
Both wget and curl can save under a name you choose, with -O and -o respectively. Reach for that when the site's own filename is unhelpful.
Step 7: Connect over ssh
ssh opens an encrypted session on another machine. The first time you connect to a host, ssh has no record of its key. It asks you to confirm the fingerprint.
ssh user@192.168.1.10ED25519 key fingerprint is SHA256:AbCdEf1234567890abcdefghijklmnopqrstuvwxyz12.
This key is not known by any other names.
Continue connecting? yes
Warning: Permanently added the host key to the list of known hosts.That prompt is your only chance to check the host is the machine you expect. Compare the fingerprint against one the host's owner gave you through another channel. If they match, type yes. Then ssh records the key and will not ask again. If the fingerprint changes later, ssh warns you loudly. That warning means someone may be impersonating the host.
Step 8: See what is listening with netstat
netstat lists open connections and the ports your own device is listening on. The -tuln flags ask for TCP and UDP sockets, listening only, with numbers instead of names.
netstat -tulnActive Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 127.0.0.1:8022 0.0.0.0:* LISTEN
tcp6 0 0 :::8022 :::* LISTENAn address of 127.0.0.1 means the service only accepts connections from this device. An address of 0.0.0.0 or :: means it accepts connections from anywhere on the network. That is worth knowing. Termux runs its SSH server on port 8022 by default, not the usual 22. Connect to it with -p 8022.
Quick reference
| Command | What it does |
|---|---|
ifconfig | List interfaces and their addresses |
ip addr | Show addresses in the modern layout |
ping -c N HOST | Send N packets to test reachability |
nmap -sV -p PORTS HOST | Scan ports and identify services |
curl, wget | Fetch or download a file over HTTP |
ssh USER@HOST | Open an encrypted remote shell |
netstat -tuln | List listening TCP and UDP ports |
Next steps
- Encoding and hashes to verify a file you downloaded before you open it.
- Managing packages to install the network tools used here.
- File permissions to lock down the keys that
sshkeeps in your home directory.
Test yourself on this
4 questions and 1 task where you run a real command, with the reasoning explained either way.
