Since it’s been a few weeks since we did one of these, and I’d like to have this book review finished before the end of the year, it’s time for another chapter review of Networking for Systems Administrators.
Chapter 7 is fairly short, and focuses on “Network Testing Basics.” It doesn’t cover tools so much as mind set. From a Systems Administrator point of view, when troubleshooting network issues, our goal is to determine what is coming into or going out of the server. Is the data we believe is leaving the server the data actually leaving the server? Is the data coming in the data we expect? There are plenty of tools to determine this at various levels, and in the end what we’re looking for is performance and correctness. The data should match, and the performance should be within our expected parameters. Anything outside of the norm should be investigated.
If the issue is at our end, it could be something as simple as a configuration issue with the application, or a bastion host firewall rule that shouldn’t have been turned on. If it’s not at our end, it could be related to firewall, network access control lists (ACLs,) packet filters, or even proxy services. Data can be blocked or mangled by some combination of the above, and once you can determine that it’s not the fault of your server or application, you can show the evidence to the network or firewall teams, and engage them for assistance in troubleshooting upstream from your machine. Don’t blame the firewall first. Check your own stuff first, gather evidence, then engage.