- A guide to securing your home computer system with a Linux firewall
- Is your home system at risk?
- What's safe?
- Is your home system a server?
- Are broadband connections more vulnerable?
- What ports are open?
- Using netstat to list ports
- Is Windows file sharing a risk?
- Using a port scan to test your system
- Checking for Windows NetBIOS risks
How do you know if your computer is vulnerable?
Each IP address is accessed through a port address in the numeric range of 0-65535. A server on your computer will "listen" to a specific port and respond to requests that come into that port.
The only ports that are vulnerable are those that have servers responding to them. Some of the ports are assigned for network services like port 80 for HTTP (the web), port 21 for FTP (file transfer protocol), port 110 for mail, and so on. The assigned ports are detailed in RFC1700. The list of assigned ports starts on page 16 of RFC1700. The assigned ports are in the range of 0-1023.
Don't think that you only have to worry about the assigned ports, though. The unassigned ports are commonly used for many server functions such as secure transactions on the web.