ngrep

Filter network traffic packets using regular expressions. More information: https://github.com/jpr5/ngrep.

Capture traffic of all interfaces:

ngrep -d any

Capture traffic of a specific interface:

ngrep -d {{eth0}}

Capture traffic crossing port 22 of interface eth0:

ngrep -d {{eth0}} port {{22}}

Capture traffic from or to a host:

ngrep host {{www.example.com}}

Filter keyword 'User-Agent:' of interface eth0:

ngrep -d {{eth0}} '{{User-Agent:}}'