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Essential network commands

When the network misbehaves, these commands tell you exactly what's wrong. They're built into Windows, macOS and Linux: open Command Prompt (Windows: press Win, type cmd) or Terminal.

1. See your own settings: ipconfig / ip

Windows

ipconfig
ipconfig /all

Linux / macOS

ip addr        (Linux)
ifconfig       (macOS / older Linux)

Look for:

Field	Example	Meaning
IPv4 Address	192.168.1.23	Your device's address
Subnet Mask	255.255.255.0	Your network size (/24)
Default Gateway	192.168.1.1	Your router
DNS Servers	8.8.8.8	Who turns names into IPs
Physical Address	3C-52-82-1A-4F-9E	Your MAC address

If your IPv4 address starts with 169.254, your device did not get an address from DHCP. Check the cable, Wi-Fi or router.

Useful fixes on Windows:

ipconfig /release
ipconfig /renew       (ask DHCP for a new address)
ipconfig /flushdns    (clear old DNS answers)

2. Can I reach it? ping

ping 192.168.1.1
ping google.com
ping -n 10 8.8.8.8      (Windows: 10 pings)
ping -c 10 8.8.8.8      (Linux/macOS)

Sample reply:

Reply from 8.8.8.8: bytes=32 time=38ms TTL=117

time: the round trip in milliseconds. Under 50 ms is great; over 200 ms feels slow.
Request timed out: no reply (the device is off, unreachable, or blocks ping).
Some lost packets means an unstable connection (weak Wi-Fi, bad cable).

The classic troubleshooting ladder

ping 127.0.0.1 : is my network card/software OK?
ping <my IP> : is my address set up?
ping <gateway> : can I reach the router? (If not: cable/Wi-Fi/LAN problem.)
ping 8.8.8.8 : can I reach the internet by IP? (If not: router/ISP problem.)
ping google.com : does DNS work? (If 4 works but 5 fails: DNS problem.)

3. Where does it break? tracert / traceroute

tracert google.com       (Windows)
traceroute google.com    (Linux/macOS)

It lists every router ("hop") on the way. If the list stops at hop 2, the problem is near you or your ISP; if it goes far and then stops, it's further away.

4. Is DNS working? nslookup / dig

nslookup marzleytechsolutions.co.ke
nslookup marzleytechsolutions.co.ke 8.8.8.8     (ask Google's DNS instead)
dig marzleytechsolutions.co.ke                   (Linux/macOS, more detail)

Use it after changing domain records to see if they've updated.

5. Who is talking? netstat / ss

netstat -an           (Windows/macOS: all connections and listening ports)
netstat -ano          (Windows: with process IDs)
ss -tulpn             (Linux: listening ports and programs)

Great for "is my web server actually listening on port 80?"

6. Others worth knowing

Command	Use
`arp -a`	Devices your computer has talked to on the LAN (IP ↔ MAC)
`hostname`	Your computer's name
`getmac`	MAC addresses (Windows)
`pathping google.com`	ping + tracert combined (Windows)
`curl -I https://example.com`	Check a website's response headers
`Test-NetConnection example.com -Port 443`	PowerShell: is a port open?

Practice scenario

A user says "the internet is not working". You run:

ipconfig shows 169.254.10.4 → no DHCP. Check the cable/Wi-Fi and router.
Address is fine, ping 192.168.1.1 works, ping 8.8.8.8 fails → the router or ISP line is down. Restart the router, check the ISP.
ping 8.8.8.8 works, ping google.com fails → DNS. Set DNS to 8.8.8.8 / 1.1.1.1 or run ipconfig /flushdns.

Why network commands matter

"The internet is down" can mean many different problems: a loose cable, Wi-Fi with no internet, an expired data bundle, a DNS failure, a router fault, a blocked website or a problem at the ISP. Network commands let you find where the problem is in minutes instead of guessing, and give you facts to report to the ISP or your manager. Help desk staff, ICT officers, network engineers and developers use them every day.

A systematic troubleshooting approach (bottom-up)

Step	Check	Command / action
1. Physical	Cable plugged in? Wi-Fi connected? Lights on the router?	Look; reconnect
2. IP address	Did the device get a valid address?	`ipconfig` / `ip a`
3. Local network	Can you reach the router (gateway)?	`ping 192.168.1.1` (your gateway)
4. Internet	Can you reach an outside IP?	`ping 8.8.8.8`
5. DNS	Do names resolve?	`nslookup google.com`
6. Application	Does the website or app itself work?	Try another site, browser or device

Stop at the first step that fails: that's where the problem is.

Reading ipconfig /all

Windows IP Configuration
   IPv4 Address. . . . . . . . . . . : 192.168.1.23
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.1
   DHCP Server . . . . . . . . . . . : 192.168.1.1
   DNS Servers . . . . . . . . . . . : 192.168.1.1
   Lease Obtained. . . . . . . . . . : ...
   Physical Address. . . . . . . . . : 3C-52-82-1A-9F-04

Clue	Meaning
Address starts with `169.254.`	DHCP failed: the device gave itself an address. Check cable/Wi-Fi and router DHCP
No default gateway	Can't reach other networks
Gateway in a different subnet	Misconfigured static IP
Unexpected DNS server	Could be misconfiguration or malware changing settings

Fixing common address problems

ipconfig /release        # give up the current DHCP address
ipconfig /renew          # ask for a new one
ipconfig /flushdns       # clear cached DNS answers (fixes some "site not found" issues)
netsh winsock reset      # reset network stack (admin; restart afterwards)

Linux: sudo dhclient -r && sudo dhclient or restart NetworkManager; flush DNS cache with resolvectl flush-caches on systemd-resolved systems.

Understanding ping results

Reply from 8.8.8.8: bytes=32 time=24ms TTL=117
Request timed out.
Destination host unreachable.

Result	Likely meaning
Replies with low time (under ~50 ms locally)	Connection OK
High or very variable times	Congestion, weak Wi-Fi, overloaded link
Some "Request timed out"	Packet loss: unstable connection
All time out	No route, device off, or ICMP blocked by a firewall
"Destination host unreachable" from your own IP	Your device has no route (no gateway or link down)

Some servers block ping on purpose, so a failed ping isn't always proof the server is down. Try opening the service (e.g. the website) too.

ping -n 20 8.8.8.8       # Windows: 20 pings to measure packet loss
ping -c 20 8.8.8.8       # Linux/macOS
ping -t 8.8.8.8          # Windows: continuous (Ctrl+C to stop), useful while testing cables

traceroute: finding where delay starts

tracert google.com       # Windows
traceroute google.com    # Linux/macOS
mtr google.com           # Linux: live traceroute + ping statistics combined

Each line is a router ("hop"). If delays jump at hop 2 or 3 (your ISP's network), the problem is likely with the ISP; at hop 1, it's your local router or Wi-Fi. Asterisks (* * *) on a hop often just mean that router doesn't reply to traceroute.

DNS tools in depth

nslookup marzleytechsolutions.co.ke            # ask your default DNS server
nslookup example.co.ke 8.8.8.8                 # ask Google DNS directly (compare answers)
nslookup -type=mx example.co.ke                # mail servers for a domain
dig example.co.ke +short                       # Linux/macOS: concise answer
dig example.co.ke MX
dig example.co.ke TXT                          # SPF/verification records

Record	Purpose
A / AAAA	Domain → IPv4 / IPv6 address
CNAME	Alias to another name
MX	Mail servers
TXT	Verification, SPF, DKIM, DMARC for email
NS	Which name servers are authoritative

When a new website "doesn't work" after changing hosting, comparing DNS answers from different servers shows whether the change has propagated.

Ports and connections

netstat -ano | findstr :443          # Windows: who uses port 443 (PID in the last column)
ss -tulpn                            # Linux: listening ports and the programs using them
Test-NetConnection example.co.ke -Port 443    # PowerShell: is a port reachable?
curl -I https://example.co.ke        # fetch only headers: status code, server, redirects

curl -I quickly shows if a site returns 200 OK, a redirect (301) or an error (500).

Speed and Wi-Fi checks

Run a speed test (e.g. speedtest.net or fast.com) on cable and on Wi-Fi to compare.
netsh wlan show interfaces (Windows) shows Wi-Fi signal %, channel and link speed.
Test at different times: evening slowdowns often mean ISP congestion.

Writing a useful fault report for an ISP

Since 9:00 am, all devices on our network lose internet. Router lights normal. ping 192.168.1.1 OK (2 ms). ping 8.8.8.8: 40% packet loss, times 300–900 ms. tracert shows delays starting at hop 2 (your gateway 41.x.x.x). Speed test: 2 Mbps on a 40 Mbps plan. Account number: ...

Clear facts get faster, more useful support.

Practice

Run ipconfig /all (or ip a) and identify your IP, gateway, DNS and MAC address.
Ping your gateway, 8.8.8.8 and google.com 20 times each and compare times and packet loss.
Run a traceroute to a Kenyan website and to an international one; compare hop counts and times.
Look up the MX and TXT records of a domain you know.
Use curl -I on three websites and note their status codes and redirects.

Think about it: A user can open websites by IP address but not by name, and other users on the same network are fine. What would you check?Show answer

This points to a DNS problem on that one device: check its DNS settings in ipconfig /all (a wrong static DNS server, VPN or malware changes), flush the DNS cache (ipconfig /flushdns), test with nslookup google.com 8.8.8.8, and check the hosts file for unexpected entries.

Check yourself

Which Windows command shows your IP address, gateway and DNS?
Show answer
ipconfig
Your address starts with 169.254. What service failed to give you an address?
Show answer
DHCP
ping 8.8.8.8 works but ping google.com fails. What is the problem?
Show answer
DNS
Which command lists every router on the way to a website on Windows?
Show answer
tracert
Which command asks DNS for a domain's IP address?
Show answer
nslookup
Which Windows command clears the local DNS cache?
Show answer
ipconfig /flushdns
Which DNS record type lists a domain's mail servers?
Show answer
MX
Which Linux command shows listening ports and the programs using them? (two letters plus options allowed)
Show answer
ss
What is the first device you should ping to test the local network? (two words)
Show answer
default gateway

Lesson 20 of 24 in Networking · Printable course notes