NDT and NPAD are both web100-based tools that will run a throughput test and try to tell you what the bottleneck is. There are a number of public NDT and NPAD servers, and both are included in the perfSONAR Toolkit.
Find a server:
Both NDT and NPAD work best if you find the server closest to you. For NPAD, use an RTT value that matches the longest path you are trying to use.
Both NDT and NPAD have command line versions of the tools that are useful for when you want to run a test from a host other than your desktop. Download and installed the tools from the sites linked above, and then run:
web100clt -n hostname -b buffer_size
e.g.: web100clt -n myhost -b 4194304
or for more details:
web100clt -n myhost -ll -b 4194304
diag-client server_name port target_RTT target_data_rate
e.g.: diag-client hostname 8100 50 500