nload

BSD (kvm) network load monitor

Uses (Open)BSD kvm interface to monitor network load in a vmstat(1) like fashion
Reports kilobit/second and packets/second seen by the specified interface
Freeware, unrestricted public domain software. (whaddaya expect, it's like 10 lines!)

Q: nload says it can't open kvm: Permission denied.
A: This is expected, since only root should be able to read kernel memory, become root.