What's the best way to test and monitor your network devices?

While both of these tools can be immeasurably helpful when troubleshooting a network issue they require that you have identified a problem before you can use them effectively (though traceroute can be used to get an idea of the path traffic takes without continuous data collection and analysis its benefits beyond specific troubleshooting is questionable). Both tools (plus many more) are available on pretty much any system you have (Linux, Mac, Windows, etc.) and work about the same (though of course every vendor makes little tweaks) making them easy to use and readily available. While these tools can be immensely helpful a broader monitoring solution will provide easier access to similar data plus far more functionality.

I love flow (NetFlow, sFlow, etc.) sources. They have many of the benefits of packets without the challenges that come with packets. You can collect vast amounts of data far beyond what is listed. Flow is excellent as a source of data for visibility tools and security tools. While SNMP is old (1988) it is ubiquitous - pretty much everything supports it (servers, laptops, printers, access points, etc.) making it incredibly useful for monitoring things like availability, capacity, performance, and more. While SNMP is the current standard there have been numerous attempts to replace it with something more modern. The current contender (streaming telemetry) seems to be making some inroads but is nowhere near as universal as SNMP at this time.

Tools like Wireshark are great if you know about packets (and even if you are only a beginner). It can decode a variety of traffic providing detailed information and analysis of what is happening.. With the proper plugins you can even do things like replay SIP phone calls. Wireshark allows you to capture locally and review previously captured packet data. This allows for packets to be captured separately from the analysis since you are unlikely to have Wireshark on every system whereas other lightweight packet capture solutions may be already available to you. The biggest challenge with Wireshark is that it can be a lot. While it is great at many things a broad network monitoring solution is likely to be more helpful in daily activities.

All of the stuff outlined in this article are pretty accurate but incredibly oversimplified. The listed specific tools (nmap, etc.) all work as described but suffer from various limitations and challenges when used in real-world scenarios, especially when you move away from specialized troubleshooting (i.e. when you are looking for general monitoring/observability/visibility as opposed to troubleshooting a specific, narrow problem. My primary advice is to look at the various providers of visibility solutions (don't get caught up on whether it is visibility, observability, monitoring or something else - they are just buzzwords) and find the one(s) that meet your specific needs. Feel free to hit me up with questions if you have them!