Bandwidth Monitoring Tools for FreeBSD and Linux: iftop

Bandwidth represents the capacity of the connection. The greater the capacity, the more likely that greater performance will follow, though overall performance also depends on other factors, such as latency.

iftop is a free open-source tool to measure bandwidth utilization on the network interfaces on your systems. As the name predicts, iftop is what "top" utility is for CPU usage measurement.

To install iftop in CentOS, Fedora, RHEL ( make sure you have DAG repository enabled ):

# yum install iftop

To install iftop in FreeBSD:

# cd /usr/ports/net-mgmt/iftop
# make install clean

To install iftop in Ubuntu/Debian:

# sudo apt-get install iftop

Starting iftop:

# iftop -i if

where if is the network interface.

Example:

# iftop -i eth0