How To Telnet Udp Port Windows

Checking if a port is open up interactively or through a script is quite a common operation for whatever administrator. There are all sorts of reasons y'all might desire to practise this:

Cheque if a web server is downwards.
Bank check if a printer is working.
Check if a firewall is blocking a port.
Bank check if an SMTP Server is reachable etc.

You lot can test for open ports using a variety of different tools all of which have their pros and cons.

Telnet
Portqry.exe
Powershell Test-NetConnection

Using Telnet to test for open up ports

This is the probably the virtually common method to bank check for an open port. Unfortunately Microsoft stopped including the telnet client by default on Windows Server, so you will demand to install the telnet client beginning if information technology is non already installed.

The full general syntax is: "telnet host portnumber". If you practise not specify a port number it will attempt to connect to the host on port 23, which is the standard telnet port.

Telnet example to Check an SMTP Server

You tin bank check if a server has SMTP server running and available by using telnet to connect to port 25. In this example I am testing connection to my own postal service server which is on Role 365:

telnet tachytelic-net.post.protection.outlook.com 25

If yous can successfully connect y'all will run into a response from the mail service server:
Image showing telnet client being used to check if SMTP server is responding You can even manually send an e-mail message directly to the SMTP server interactively using telnet.

Telnet example to bank check a Web Server

You tin can connect to a Web server on port 80 to check that it is serving requests:

telnet world wide web.tachytelic.net 80

In the case of a webserver you volition probably merely receive a blinking cursor while it waits for some input, merely this does betoken a successful connection and that the port is open up. You lot tin can take it a footstep further past issuing a HTTP Request with telnet, for example:

Get /2018/12/e-mail-vbscript-vba-office-365/ HTTP/ane.1 host: www.tachytelic.internet

I get a response from the server issuing a 301 redirect sending me to the HTTPs version of the same page:

Image showing web server response to a HTTP Get issued via the telnet client

Telnet case to check a printer

You can check if a printer is working (and actually impress to it) using telnet. Many printers will have port 9100 open for HP Jetdirect style press. My printer is on 192.168.250.34. So if I run the telnet command:

telnet 192.168.250.34 9100

I volition come to a flashing cursor while the print server embedded in my HP Printer waits for input. If I type "This is a examination" and so quit telnet it prints a page with those words on it.

Advantages of using telnet

Quick and easy to exercise a port test
Interactive so you can do more extensive testing of certain services.
More or less bachelor on any operating system.

Disadvantages of using telnet

It is interactive, and then information technology is not suitable for automated tests.
Non installed past default on recent versions of Windows. But easy to install, follow these instructions.
Not useful for bank check UDP ports.

Using Portqry.exe to exam for open ports

Portqry.exe is an old tool only still works well and has extensive options for port testing. It's much easier to use within scripts or automated checks. It can be used to cheque multiple ports in a single command and makes information technology piece of cake to check UDP ports as well as TCP ports.

Case Portqry command to check a single port on a spider web server

In this example I am checking port 443 (https) of this web log:

portqry -n www.tachytelic.net -p tcp -due east 443

Here yous can run across the test was successful: Image showing successful test of a web server on port 443

Example Portqry to check multiple ports on a Web server

This example shows how to use Portqry to examination multiple ports at the aforementioned time, in this case ports 80 and 443:

portqry -north www.tachytelic.net -p tcp -o lxxx,443

Again, the results are good:
Image showing the usage of portqry.exe to test multiple ports on a web server

Example Portqry to check an SMTP Server

Portqry is aware of some types of applications and can show you additional data returned from the server, SMTP is a good example:

portqry -n tachytelic-net.postal service.protection.outlook.com -p tcp -e 25

As you can encounter from the screenshot, Portqry.exe returns the initial response from the SMTP Server:
Image showing use of portqry.exe to test an SMTP Server with additional response message received from the server

Portqry.exe is excellent for scripting because of the vast number of options and that information technology can operate in placidity mode where information technology volition simply return a status code, which is exactly what you would desire if you were building this into a script. Portqry.exe has many options so it is well worth reading the documentation.

Advantages of using Portqry.exe

Easy to employ.
Many options for checking both TCP and UDP ports.
Quiet mode is fantabulous for scripting.
Very fast.

Disadvantages of using Portqry.exe

It is not installed past default.
It is onetime software, but nevertheless works perfectly on recent operating systems.

Using Powershell Test-NetConnection to test for open ports

You tin also use Powershell to test for open ports and this is a great choice considering it works well both interactively and for usage within a script. It's congenital in to recent versions of Powershell and it is very easy to use.

Example Exam-NetConnection Powershell to bank check a single port on a Web server

Again, this code shows how to exam port 443 of this blog using Powershell:

Test-NetConnection -ComputerName www.tachytelic.net -Port 443

Here is the output of the successful test:
Image showing output of Powershell Test-NetConnection to test if a web server port is available

Example Examination-NetConnection Powershell to bank check an SMTP Server

Examination-NetConnection -ComputerName tachytelic-net.post.protection.outlook.com -Port 25

And the successful output:
Image showing how to Test SMTP Ports using Test-NetConnection with Powershell

Advantages of using Examination-NetConnection

Built in to contempo versions of Windows
Great for scripting if you lot are already using Powershell
Quick and Easy

Disadvantages of using Exam-NetConnection

Not available on all versions of Windows by default.
Just bachelor via Powershell – which isn't a problem, but might not fit in with some of your existing scripts.

Source: https://www.tachytelic.net/2018/12/test-open-ports/

Posted by: robinsontheessale1962.blogspot.com