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1. #How to use port forward network utilities how to#
2. #How to use port forward network utilities windows#

Let’s use nmap to see if port 53 (DNS) is listening on the Google DNS service (IP address 8.8.8.8)

#How to use port forward network utilities how to#

I have explained what NMAP is and how to use it in the articles here and here.īasically with nmap you can send TCP packets to specific remote ports and listen to the reply packets to verify if the port is open or closed. Now, let’s try to “ping” (connect) to a random port (e.g 12345) which is probably closed:Īs you can see from above, port 12345 does not respond to our telnet request which means it’s closed. The reply from Google is “ Connected” which means that port 443 is open. Telnet 443 <- you can specify which port to telnet (443 in this example)Īs shown on the screenshot above, I have used “telnet” to connect to at port 443. However, you can specify the destination (remote) port that you want to connect to. It has its origins back to 1969 (from when the Internet was born) and provides a text-based (command line) terminal for interacting with remote systems.īy default, the telnet protocol uses port 23 to connect to the remote system. Telnet is a popular (and very old and unsecure) protocol to connect remotely to systems (e.g to network devices, Linux machines etc). Let’s see three ways to check if a port is open: Using Telnet

In this article, I’m just using the term “ ping the port” in the context of “ poking the port” to verify if it’s open (listening) or not. The ping protocol does not send TCP packets to the remote host to identify open ports. The “Ping” protocol is actually using ICMP packets (echo, echo reply etc) to identify if a remote host is “alive” (i.e connected to the network and replying to the ICMP packets). To be accurate here, the term “ping the remote port” is not actually a valid statement. If you try to “ping” the remote ports (i.e try to communicate with the ports) and you get no-response, it means the problem is on the network between your end and the server (maybe a firewall problem, network routing problem etc). One of the first things to check is whether the remote web server’s TCP port 80 or 443 are open and reachable from your end. If you want to troubleshoot connectivity issues from your local computer/server towards a remote host, it’s better to start working from the lower OSI layers and more your way up to identify the problem.įor example, let’s say a remote web server does not respond to HTTP requests (i.e you have started your browser and visited the remote URL with no response).

#How to use port forward network utilities windows#

Web Service: Ports 80 (HTTP), 443 (HTTPs).This is a popular troubleshooting method to identify if a specific service or application is running on a remote server or computer.Īs you might know already, when an application or service is running on a host, it has a specific TCP or UDP port associated to it in order to communicate over a TCP/IP network (i.e in order for the service to send and receive TCP/IP packets over the network).įor example, some popular (well-known) services use the following TCP ports: In this article I’ll describe a few ways to verify over the network if a remote TCP port on a host is open or not.