Shell-Kernel-TCP port test

Preface

In this document I’ll try to describe how to do simple test of remote TCP port check with help of Linux kernel.

This test can be performed in case that it’s not possible to use better test like:

# nc
# telnet
# ….

This method has been tested with:

Linux kernel   - Successful
Mac OS X       - Successful
HP Unix        – Without Success

Test TCP port Connection

To test TCP connection to remote server it is possible to use Linux Kernel in this way:

# IP=<Destination_IP> ;                                                        # IP where to connect
# TCP_Port=<Destination_TCP_Port> ;                                            # TCP port where to connect

# $(echo> /dev/tcp/$IP/$TCP_Port)>/dev/null 2>&1  && echo "Successful connected" || echo "NOT Successful connected"

Example - Successful

# IP="127.0.0.1" ;                                                              # IP where to connect
# TCP_Port="22" ;                                                               # TCP port where to connect

# $(echo> /dev/tcp/$IP/$TCP_Port)>/dev/null 2>&1  && echo "Successful connected" || echo "NOT Successful connected"

Successful connected                                                            # Result of the test

Example - Unsucessful

# IP="127.0.0.1" ;                                                              # IP where to connect
# TCP_Port="2222" ;                                                             # TCP port where to connect

# $(echo> /dev/tcp/$IP/$TCP_Port)>/dev/null 2>&1  && echo "Successful connected" || echo "NOT Successful connected"

-bash: connect: Connection refused                                              # If it's possible it will provide you the reason
-bash: /dev/tcp/127.0.0.1/2222: Connection refused                              # Way it was not possible to connect
NOT Successful connected                                                        # Result of the test
Navigation
Print/export
QR Code
QR Code wiki:programming_languages:shell:shell-kernel-tcp_port_test (generated for current page)