How can I trace the macOS network stack? In safari, and several other products, I get a network timeout where I have to reload the page, even though I have a full / working Wifi connection.

This is a sporadic issue. 

The problem seems to occur after I installed Cisco's security product "OpenDNS Umbrella".  Removing OpenDNS Umbrella seems to fix the problem.

I would like to get a better understanding of the network layers in macOS so I can create an appropriate trace/diagnostic for review. 


What are the "layers" of software that are available for extension and modification in macOS?  (I'm from a Windows Mindset and understand MSFT's well-documented network API, packet filters, and what extensions are available etc). 
How can I create a trace of network activity at the aforementioned layers? For example, I want to see not just DNS traces, but any internal firewall that could be affecting me?  (macOS has a built-in firewall that might be giving me trouble.)


I did briefly install "Little Snitch" firewall program, but I then uninstalled it.  I'm not sure if this is relevant, but it does manage connections via an API I'm not aware of.
Try to install Wireshark.  Maybe monitoring the actual network activity will give you a clue (it will probably show an outgoing packet or connection that isn't answered).