TCPlooking

TCPlooking is a network diagnostic tool used to determine the state of a TCP connection between two hosts. It is part of the tcpdump suite of tools and is commonly used by network administrators and engineers to troubleshoot network issues. The tool sends a TCP SYN packet to a specified port on a target host and waits for a response. Depending on the response, TCPlooking can determine whether the port is open, closed, or filtered.

The tool is particularly useful in identifying network connectivity issues, such as firewalls blocking traffic or network devices dropping packets. It can also be used to scan a range of ports on a host to identify which services are running and accessible.

TCPlooking operates by sending a TCP SYN packet to the target port. If the port is open, the target host will respond with a TCP SYN-ACK packet. If the port is closed, the target host will respond with a TCP RST packet. If no response is received, the port is considered filtered, which can indicate the presence of a firewall or other network security device.

The tool is typically used from the command line and requires the user to specify the target host and port. It can also be used to scan a range of ports by specifying a port range. The output of the tool provides detailed information about the state of each port, including the response time and any error messages.

TCPlooking is a valuable tool for network administrators and engineers, providing a quick and effective way to diagnose network issues and ensure the proper functioning of network services. However, it should be used responsibly and ethically, with proper authorization and in compliance with all relevant laws and regulations.