[jlmcguire]

MTR is a useful tool but it is a somewhat common source of illusory issues since it generates so many icmp time exceeded packets that routers stop replying to other folks running traces. It's important, as others said, to understand that these aren't testing the data path of a network but instead the control plane path.

[cootsnuck]

What tools exist for people to test the data path of network reliably? In my experience MTR has worked well enough to approximate network routing issues. But it has always felt like a blunt tool given it can't do anything about hops with firewalls.

[jlmcguire]

It's tough. iperf is a reasonable tool. It works by setting up tcp connections and actually transferring data.

I like the work https://fasterdata.es.net/ does. They provide clear guides and set expectations if you want to get more bandwidth out of a connection.