Linux – Iftop

iftop command listens to network traffic on a named network interface, or on the first interface it can find which looks like an external interface if none is specified, and displays a table of current bandwidth usage by pairs of hosts. iftop is a perfect tool for remote Linux server over ssh session.

iftop must be run by the root or the user who has sufficient permissions to monitor all network traffic on the network interface.
Type iftop command at tge shell prompt to display traffic:

# iftop

However, iftop works best when you use filters. For example, if you want to find out how much bandwidth users are wasting or trying to figure out why the network is slow,

# iftop -f icmp

You can display or analyses packet flowing in and out of the network:

# iftop -F

Disable output for DNS traffic by using filter code such as:

# iftop -f 'not port domain'

iftop has many options read man page for further information.