Port Scanning Explained

<<-- Port Scanning -->>

What is a Port Scanner?
A Port Scanner is an application that scans specific or a range of ports to determine which are open, closed or filtered. We can compare this anology as having a door to each room. Every serivce (application) running on the system has a predefined port number assigned to it. The door will be the port number and the room will be the application. Someone can "portsweep" for multiple hosts and determine which port is listening on a specific service. For example, one can portsweep Port 80 to discover web browsing flaws. A light port scan will make a scan more quickly than a full scan.

Port Scanning can be an illegal action in certain countries. Most system administrators checks the logs as a daily routine to determine whether there has been an attempt. I would suggest that you sign a contract between you and the person you've going to port scan as you don't want to get into trouble.

Ports come in two different flavours: The TCP (Transmission Control Protocol) and UDP (Userdatagram Protocol). TCP can be described as "connection oriented" whilst UDP is "connectionless". They both rely on the protocol stack where today it is commonly known as "TCP/IP" stack.

There are a total of 65536 ports available and are assosiated by the (Internet Assigned Numbers Authority) IANA.

Since UDP is an unreliable port it will require more time to scan than TCP.

Some Port Scanners will just tell you which ports are open and closed whilst others will give you a brief explanation on that port and what type of exploit can be attempted with it.

Apart from that, Port Scanners can determine what Operating System you're using and information about that particular service (port).

Two commonly known Port Scanners are nmap and Nessus which are both open source. Originally nmap was designed to scan larger networks, although even single hosts can be scaned also. Nmap makes use of raw IP packets in novel to conlude which hosts are on the network, what services are being offered, Operating System version, types of packets filters/firewalls and more. Nmap can be downloaded freely and is open source. Both command line and Graphical User Interface (GUI) exist. The open source falls under the agreement of the GNU GPL.

Nessus is also a reliable port scanner and can provide certain amount of valuable information. These two are both the best Port Scanners there are out there nowadays.

If you don't want to install a Port Scanner on your system, one can easily use a Web based Port Scanner to scan a system and draws a picture on how it looks at the other side of the Internet. These Web based Port Scanners scan quickly and provide you with the essential information only.

Google for "Web Based Port Scanner" or "free online Port Scanner" to use one.

Until next time,
DarkSolo