5 ms·

Basic Network Troubleshooting

118 points by zdw 5y ago

InvaderFizz 5y ago
This is a pretty good write up. I've taken to use a very similar scenario as part of my interview process for candidates. It's shocking how few SRE candidates I interview can walk me through a simple scenario such as troubleshooting this. I don't even require the correct incantation of curl/openssl/dig/nslookup/nc/route/etc, I just want to see their process for breaking down the problem and searching for the fault. The most common thing that I see is changing the local DNS resolver, flushing the DNS cache, rebooting the local computer, disabling the local firewall, and then giving up. I start with NXDOMAIN because the subdomain is not configured on Route53, then it gets progressively more weird from there. NACL blocking return traffic, apache/nginx service is just dead and systemd didn't restart it, apache/nginx is bound to 127.0.0.1:80/443, self signed cert with an invalid CommonName. Each problem presents a jumping off point to dive deeper into different areas.
teleforce 5y ago
This book by Michael Lucas is an indespensible guide for those who are not network engineers or network administrators themselves: Networking for System Administrators: https://mwl.io/nonfiction/networking#n4sa https://mwl.io/nonfiction/networking#n4sa
- blondin 5y ago
  thank you so much for recommending. i checked the table of contents and this is really my kind of book.
- arittr 5y ago
  Seconded - this book is a must read for any software engineers that work with the internet (in my opinion)
  - bennysomething 5y ago
    Thanks for this recommendation, having not studied networking at university I've always struggled with it.
- vsnf 5y ago
  I just purchased this on the backs of the sibling comments. I've never had an adequate understanding of networking but have found myself in so many situations where it would have saved me from embarrassment in front of clients and wasted hours in front of the terminal. I have high hopes for the book.

118 points by zdw 5y ago

This is a pretty good write up. I've taken to use a very similar scenario as part of my interview process for candidates. It's shocking how few SRE candidates I interview can walk me through a simple scenario such as troubleshooting this. I don't even require the correct incantation of curl/openssl/dig/nslookup/nc/route/etc, I just want to see their process for breaking down the problem and searching for the fault. The most common thing that I see is changing the local DNS resolver, flushing the DNS cache, rebooting the local computer, disabling the local firewall, and then giving up. I start with NXDOMAIN because the subdomain is not configured on Route53, then it gets progressively more weird from there. NACL blocking return traffic, apache/nginx service is just dead and systemd didn't restart it, apache/nginx is bound to 127.0.0.1:80/443, self signed cert with an invalid CommonName. Each problem presents a jumping off point to dive deeper into different areas.

teleforce 5y ago

This book by Michael Lucas is an indespensible guide for those who are not network engineers or network administrators themselves: Networking for System Administrators: https://mwl.io/nonfiction/networking#n4sa https://mwl.io/nonfiction/networking#n4sa

blondin 5y ago
thank you so much for recommending. i checked the table of contents and this is really my kind of book.
arittr 5y ago
Seconded - this book is a must read for any software engineers that work with the internet (in my opinion)
- bennysomething 5y ago
  Thanks for this recommendation, having not studied networking at university I've always struggled with it.
vsnf 5y ago
I just purchased this on the backs of the sibling comments. I've never had an adequate understanding of networking but have found myself in so many situations where it would have saved me from embarrassment in front of clients and wasted hours in front of the terminal. I have high hopes for the book.