I Scanned My Own Network — Here's What I Found

Running nmap for the first time is humbling. You realise how much is quietly "open" in your own home.

I downloaded nmap, typed one command against my home network, and stared at the results for a full five minutes. I had no idea my smart TV was running an HTTP server. Or that my router had Telnet open — a protocol from 1969 that sends passwords as plain text. This is what I did, what I found, and what it means.

What is nmap?

nmap (Network Mapper) is a free, open-source tool used by security professionals and attackers alike to discover devices on a network and find out which services are running on them. When you run nmap against an IP address, it sends carefully crafted packets to a range of ports and analyses the responses to determine what's open, what's closed, and what's filtered by a firewall.

It's completely legal to scan your own network. Never scan a network you don't own or have explicit written permission to test.

Step 1 — find your own IP range

Before scanning, you need to know what IP range your home network uses. On Linux or Mac, run:

ip addr show        # Linux
ifconfig            # Mac
ipconfig            # Windows

You'll see something like 192.168.1.45 with a subnet of /24. That means your network is 192.168.1.0/24 — addresses from 192.168.1.1 to 192.168.1.254. That's your scan target.

Step 2 — run your first scan

# Discover all live devices on your network
nmap -sn 192.168.1.0/24

# Scan top 1000 ports on all found devices
nmap 192.168.1.0/24

# Get service versions and OS info (more detailed)
sudo nmap -sV -O 192.168.1.0/24

# Save results to a file
sudo nmap -sV 192.168.1.0/24 -oN my_scan.txt

Step 3 — reading the output

Here's what a typical scan result looks like, and what each part means:

Nmap scan report for 192.168.1.1
Host is up (0.0023s latency).

PORT     STATE  SERVICE   VERSION
22/tcp   open   ssh       OpenSSH 8.4p1
80/tcp   open   http      lighttpd 1.4.55
443/tcp  open   ssl/http  lighttpd 1.4.55
53/tcp   open   domain    dnsmasq 2.85
23/tcp   open   telnet    Linux telnetd   ← ⚠ dangerous!

MAC Address: AA:BB:CC:DD:EE:FF (TP-Link)

Breaking this down:

• PORT: the port number and protocol
• STATE: open (service is running and reachable), closed (no service), filtered (firewall blocking nmap's probe)
• SERVICE: what nmap thinks is running there based on the port number
• VERSION: the actual software and version detected (only shown with -sV flag)

What I actually found on my network

When I ran this on my home network, I found 9 devices. The highlights — some alarming, some expected:

• My router (192.168.1.1): Port 80 (admin panel over HTTP, not HTTPS), port 23 (Telnet — immediately disabled this), port 53 (DNS — expected)
• My smart TV: Port 7080 open, running a service I didn't recognise. After researching: it's the TV's screen-sharing receiver. I turned it off in the TV settings.
• My laptop: Port 5000 open — a Flask development server I had forgotten to stop from a project the week before. Oops.
• My old printer: Port 80 open with a full web admin interface — accessible to anyone on my Wi-Fi, with no password set.

Why open ports matter for security

Every open port is a potential entry point. If a service running on that port has a known vulnerability — and you haven't updated it — an attacker on your network (or the internet, if the device is exposed externally) can exploit it. The printer with no password is a perfect example: anyone connected to my Wi-Fi could have changed printer settings, captured print jobs, or potentially pivoted further into my network.

What I did after the scan

1. Disabled Telnet on the router immediately — logged into the admin panel and turned it off
2. Changed the router admin panel from HTTP to HTTPS access only
3. Set a password on the printer web interface
4. Stopped the Flask development server on my laptop (Ctrl+C — I had it running in a background terminal tab)
5. Turned off the smart TV screen-sharing receiver

⚠️ Important Only scan networks you own or have explicit permission to test. Running nmap against someone else's network without permission is illegal in most countries, regardless of intent.

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What to explore next:

• nmap.org/book — free online reference
• TryHackMe: Active Reconnaissance room
• Next post: Firewall Rules Explained With Real Examples →