lsof

lsof list open files
lsof -i :22 list all ssh connections (same :ssh)
lsof -i@10.0.0.1 list all connections from 10.0.0.1
lsof -i@amsterdam.nl list all connections from domain
lsof -u username list all open files from username
lsof -c bash list open files related to bash
lsof -c /log/ list all open files from all processes containing log

iperf

iperf -s -w128k run server for performance benchmark
iperf -c <serveraddress> -w128k -t30 -r run client