If you have just bought a new (to you) nic card or other networking device and want to test that all of the ports can pass traffic at the expected rate, as long as you have nc and the firewall ports open on a “server” with a known good nic and have nc installed on your “client” device that you want to test it is very easy to test.
Of course, if you are testing a switch itself, then it is just a matter of having two known good machines to act as the client and the server and to insert the switch between them.
Ensure that you have a high port that is allowed by your firewall. On the server side run the following to set up a listening service
nc -l -k <port> > /dev/null
Then on the client run the following:
$ dd if=/dev/zero bs=1M count=1K | nc -vn <server-ip-addr> <port>
Connection to <server-ip-addr> <port> port [tcp/*] succeeded!
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 9.0998f s, 118 MB/s
Then, just remember to multiply the MB copied to the server by 8 to get the rate in megabits/s.