Regardless of whether you work on the front-end or back-end, I think all developers should gain some proficiency in network troubleshooting. This is especially true if you find yourself gravitating towards lower level systems programming.
The ability to troubleshoot the network and systems separates good developers from great developers. Great developers understand not just code abstraction, but understand the TCP/IP model:
Some basic network troubleshooting skills
If you are just getting into networking, here are some basic tools you should add to your toolbelt:
- Perform a DNS query (e.g.
- Send an ICMP echo request to test end to end IP connectivity (i.e.
- Analyze the various network hops (i.e.
- Check whether you can establish a TCP socket connection (e.g.
telnet X.X.X.X [port])
- Test application layer (i.e.
- Perform a packet capture (e.g.
tcpdump -i any) and what bits are sent on the wire
What IP address is my browser connecting to?
% dig dev.to ; <<>> DiG 9.10.6 <<>> dev.to ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39029 ;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 512 ;; QUESTION SECTION: ;dev.to. IN A ;; ANSWER SECTION: dev.to. 268 IN A 18.104.22.168 dev.to. 268 IN A 22.214.171.124 dev.to. 268 IN A 126.96.36.199 dev.to. 268 IN A 188.8.131.52
Is the web server listening on the HTTP port?
% telnet 184.108.40.206 443 Trying 220.127.116.11... Connected to 18.104.22.168. Escape character is '^]'.
Each of the above tools helps you isolate connectivity issues. For example, if your client receives an HTTP 5XX error, you can immediately rule out any TCP level issue. That is, you don’t need to use
telnet to check whether there’s a firewall issue or whether the server is listening in on the right socket: the server already sent an application level response.
Learning more about the network stack helps you quickly pinpoint and isolate problems:
- Is it my client-side application?
- Is it a firewall blocking certain ports?
- Is there a transient issue on the network?
- Is the server up and running?
I’m Matt Chung. I’m a software engineer, seasoned technology leader, and father currently based in Seattle and London. I love to share what I know. I write about topic developing scalable & fail-safe software running in the AWS cloud, digital organization as a mechanism for unlocking your creativity, and maximizing our full potentials with personal development habits.View all articles