General Information

nc or netcat “is a feature-packed networking utility which reads and writes data across networks from the command line.”.

Checklist

• Distro(s): Any

EL6

• -n → do not perform DNS lookups
• -u → use UDP instead of default TCP
• -v → verbose
• -w 3 → wait 3 seconds before timeout of initial connection
• -z → Scan only

EL7

• -n → do not perform DNS lookups
• -u → use UDP instead of default TCP
• -i → Idle read/write timeout (disconnect after successful connection)
• -v → verbose
• -w 3 → wait 3 seconds before timeout of initial connection

Netcat examples.

Test to see if you can open a connection to a port on a remote system.
This is useful to see if a firewall has correct rules.

Example: Check the remote system (192.168.1.1) for an open 443/tcp connection

• EL6

  nc -zvw 3 192.168.1.1 443

• EL7

  nc -i 3 -vw 3 192.168.1.1 443