Networking
June 29, 2026 ยท View on GitHub
- CIDR visualizer
- VPNs
- Browser Fingerprinting
- I2P
- Commands
- 3rd Party Tools
- Troubleshooting
- Diagrams
- Meme
CIDR visualizer
Shows bits, netmask, first IP, last IP, number of IPs in range.
Especially those of you who never learnt to do your IP network calculations for your CCNA upwards.
VPNs
See VPNs.
Browser Fingerprinting
fingerprint.com can still sort of identify you using a hash of common characteristics. Click the link from Incognito/Private Browsing and on/off VPN to see
Documentation:
Open source library (TODO read this code):
https://github.com/fingerprintjs/fingerprintjs
I2P
Invisible Internet Protocol.
Anonymous internet network layer to route traffic through.
Commands
Ping
Check networking connectivity between devices using ping.
Eg. check tiny basic ICMP packets can reach the well known public IP address of 4.2.2.1 to see if your router is passing traffic to the internet and back successfully:
ping 4.2.2.1
Routing
Show Routing Table
This works on Mac, Windows and Linux:
netstat -rn
Show Linux Routing Table
Only works on Linux:
route -n
Add Static Route
route add ...
ip route ...
Check the man pages for route and ip-route for details:
man route
man ip-route
DNS lookup
Look up a well known public DNS address:
On Linux or Mac:
host google.com
or more detailed:
dig google.com
On Windows:
nslookup google.com
You can check your DNS requests are actually being sent using tcpdump:
sudo tcpdump -i en0 -n port 53
For explanation of tcpdump see the Packet Tracing section below.
Public IP
Find the public IP you appear as after NAT translation
curl ifconfig.co
For geolocation and other details:
curl ifconfig.co/json
Country Phone Calling Code
curl -s https://ipwho.is/ | jq -r '.calling_code'
Software Firewall
iptables
On Linux, show your local IP Tables software firewall rules:
iptables -nL -line-numbers
Packet Tracing
To trace packets your network interface can see, use the tcpdump command:
sudo tcpdump -i en0 -n
Here en0 is my Mac's Wifi network interface.
| Switches | Description |
|---|---|
-n | do to not resolve IP addresses |
-v | verbose mode to see protocol and flags (eg. to debug TCP syn/ack responses) |
Add a "pcap filter" to only show the select type of traffic you're looking for.
Example - to see only DNS traffic on port 53 (tcp or udp):
sudo tcpdump -i en0 -nnv port 53
For full pcap-filter syntax, check the pcap-filter man page:
man pcap-filter
Network Speed Test
Local Network Speed Test
Test your local network speed between two machines.
Start iperf server on one machine:
iperf -s
Run iperf client on another machine:
iperf -c "$ip" # of above machine
Internet Network Speed Test
Network Quality
Built-in available in macOS Monterey or later:
networkquality
==== SUMMARY ====
Uplink capacity: 68.173 Mbps
Downlink capacity: 77.023 Mbps
Responsiveness: Low (322.581 milliseconds | 186 RPM)
Idle Latency: 204.167 milliseconds | 294 RPM
Speedtest.net
You can use it via:
- Website
- Apps
- CLI
I find that I generally get significantly faster speed test results when:
- using 5G wifi networks:
- perhaps due to less clients causing wifi contention since most customers are directed to use the default 2.4Hz networks
- running on Mac rather iPhone:
- perhaps due to the stronger wifi card on my Macbook Pro
SpeedTest.net App
I've started using this more because the app on iPhone and Mac records the speed test results along with which wifi network you were on at the time.
This is useful to keep a record to check back and it's also both easy to use and gives a nice GUI speedometer as well as jitter graph.
https://www.speedtest.net/apps
SpeedTest.net CLI
On Mac:
brew install speedtest
or generically
pip install speedtest-cli
If installed via Homebrew on Mac:
speedtest
If installed via Pip:
speedtest-cli
Output at one of my favourite cafe's in Vietnam:
Retrieving speedtest.net configuration...
Testing from xTom (45.14.71.20)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by xTom (Osaka) [0.00 km]: 143.447 ms
Testing download speed................................................................................
Download: 21.80 Mbit/s
Testing upload speed......................................................................................................
Add the --share switch to generate a URL to an image
speedtest-cli --share
Retrieving speedtest.net configuration...
Testing from xTom (45.14.71.20)...
Retrieving speedtest.net server list...
Selecting best server based on ping...
Hosted by Verizon (Tokyo) [395.51 km]: 126.545 ms
Testing download speed................................................................................
Download: 21.13 Mbit/s
Testing upload speed......................................................................................................
Upload: 10.67 Mbit/s
Share results: http://www.speedtest.net/result/17241162768.png
Sometimes this fails with the following error:
Retrieving speedtest.net configuration...
Cannot retrieve speedtest configuration
ERROR: HTTP Error 403: Forbidden
in which case this might help:
speedtest --secure
or just use the website, which still works in that scenario.
An alternative CLI for speedtest.net can be found at
:octocat: sindresorhus/speed-test
npm install --global speed-test
speed-test
Fast.com
Internet speed test by Netflix
:octocat: sindresorhus/fast-cli
npm install -g fast-cli
fast-cli
or if installed without the -g global switch:
~/node_modules/fast-cli/distribution/cli.js
Does download speed by default, use --upload switch for upload speed.
Optionally use --json switch to output in JSON format.
./node_modules/fast-cli/distribution/cli.js --upload --json
{
"downloadSpeed": 210,
"uploadSpeed": 18,
"downloaded": 300,
"uploaded": 80,
"latency": 74,
"bufferBloat": 131,
"userLocation": "Osaka, JP",
"userIp": "45.14.71.20"
}
3rd Party Tools
- ifstat shows network traffic by interface in a vmstat/iostat-like manner
- iftop - shows network traffic by service and host
- ettercap - network sniffer / interceptor / logger for ethernet
- bandwhich - is a terminal bandwidth utilization tool
- nettop - shows packet types, sorts by either size or number of packets
- darkstat - breaks down traffic by host, protocol, etc. Geared towards analysing traffic gathered over a longer period, rather than live viewing
- iptraf-ng - console-based network monitoring program for Linux that displays information about IP traffic
- iptstate - top-like interface to your netfilter connection-tracking table
- flowtop - top-like netfilter connection tracking tool
- BusyTasks - java-based app using top, iotop and nethogs as backend
- sniffer - modern alternative network traffic sniffer
- nettop (by Emanuele Oriani) - simple process/network usage report for Linux
- hogwatch - bandwidth monitor (per process) with graphs for desktop/web
- nethogs - top for Network Process
- nethogs-qt Qt-based GUI
- gnethogs - GTK-based GUI (work-in-progress)
Stats
See the Mac page's Stats Bar section.
Pingr
See the Mac page's Pingr section.
Troubleshooting
Wifi Issues
Wifi Capture Portal Not Loading
Try forcing it by opening this site which doesn't use SSL, therefore allowing the captcha portal to intercept and redirect to itself:
Check you haven't set explicit hardcoded DNS servers in your network settings (eg. public DNS) as this causes some local captcha portal DNS lookups to fail.
For more details, you can see the Mac page's troubleshooting section Wifi Capture Portal Not Loading.
Diagrams
From the HariSekhon/Diagrams-as-Code repo:
Network - Layer 2 - Local - ARP
Network - Layer 3 - Remote - IP
Web Basics
Browser Flow
Meme
Which Server is Fastest
