What is Port 80How Web Servers Work
On a Web server or Hypertext Transfer Protocol daemon, port 80 is the port that the server "listens to" or expects to receive from a Web client, assuming that the default was taken when the server was configured or set up. A port can be specified in the range from 0-65536 on the NCSA server. However, the server administrator configures the server so that only one port number can be recognized. By default, the port number for a Web server is 80.
"Invalid URL" messages are not uncommon and there are various reasons for receiving them. In many cases they can be resolved by clearing your browser cache
and cookies, then opening an elevated Command Prompt
and typing: ipconfig /flushdns
You can use netstat
, a command-line
tool that displays incoming and outgoing network connections to check whether or not a port is open on your system, to obtain Local/Foreign Addresses, PID and listening state.
- netstat /? lists all available parameters that can be used.
- netstat -a lists all active TCP connections and the TCP and UDP ports on which the computer is listening.
- netstat -b lists all active TCP connections, Foreign Address, State and process ID (PID) for each connection.
- netstat -n lists active TCP connections. Addresses and port numbers are expressed numerically; no attempt is made to determine names.
- netstat -o lists active TCP connections and includes the process ID (PID) for each connection. You can find the application based on the PID on the Processes tab in Windows Task Manager. This parameter can be combined with parameters -a, -n, and -p as shown below:
* Understanding the Netstat Command?
* How to Detect hackers with netstat
* Secrets of netstat usage
* How to Investigate a port in Windows and Linux
-- If the port in question is listed as "Listening" there is a possibility that it is in use by a Trojan server but your firewall, if properly configured, should have blocked any attempt to access it. A "listening
" state is when a program on a computer listens and waits on an open port to accept (establish) a connection with a remote computer on another port. See what is the Difference between Established/Listening Ports?
By default, Windows Task Manager
will not show the PID of a processes. You have to enable it from the View menu. To view the PID in Task Manager:
1. Open Task Manager and click the Processes tab.
2, Click View in the top menu and choose Select Columns...
3. Place a check mark in the box next to PID (Process identifier)
4. Click OK.
There are online port scanning
services which can be used to check for open and vulnerable ports:
* Shields Up
will alert users of any ports that have been opened through firewalls or NAT routers.
* Online Port Scan
allows you to scan individual TCP ports to determine if the device is listening on that port.
* Subnet Online Port Scanner
allows you to scan a host or IP for an open or closed TCP port.
* MxToolbox Port Scan
allows you to check what services are running and open.
* Open Port Check Tool
allows you to check your external IP address and detect open ports on your connection.
* AuditMyPc Firewall Test
will check your computer for ports that are commonly left open and could allow your computer to be compromised.
There are third party utilities that will allow you to manage, block, and view detailed listings of all TCP and UDP endpoints on your system, including local/remote IP addresses, state of TCP connections and the process that opened the port:
You can investigate IP addresses and gather additional information at: