Testing Port Connectivity

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From the course by Google

The Bits and Bytes of Computer Networking

3014 ratings

Google

The Bits and Bytes of Computer Networking

3014 ratings

Course 2 of 5 in the Specialization Google IT Support Professional Certificate

This course is designed to provide a full overview of computer networking. In this course, we’ll cover everything from the fundamentals of modern networking technologies and protocols to practical applications and network troubleshooting. By the end of this course, you’ll be able to: - describe computer networks in terms of a five-layer model. - understand all of the standard protocols involved with TCP/IP communications. - grasp powerful network troubleshooting tools and techniques. - learn network services like DNS and DHCP that help make computer networks run. Except as otherwise noted, the contents on this site are licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

From the lesson

Troubleshooting and the Future of Networking

Congratulations, you've made it to the final week in the course! In the last week of this course, we'll explore the future of computer networking. We'll also cover the practical aspects of troubleshooting a network using popular operating systems. By the end of this module, you'll be able to detect and fix a lot of common network connectivity problems using tools available in Microsoft Windows, MacOS, and Linux operating systems.

Ping: Internet Control Message Protocol5:18

Testing Port Connectivity2:43

Meet the Instructors

Google

We've covered a bunch of ways to test connectivity between machines at

the network layer.

But sometimes, you need to know if things are working at the transport layer.

For this, there are two super powerful tools at your disposal.

Netcat on Linux and Mac OS and Test-NetConnection on Windows.

The Netcat tool can be run through the command nc, and

has two mandatory arguments, a host and a port.

Running nc google.com 80 would

try to establish a connection on port 80 to google.com.

If the connection fails, the command will exit.

If it succeeds, you'll see a blinking cursor, waiting for more input.

This is a way for you to actually send application layered data to the listening

service from your own keyboard.

If you're really only curious about the status of a report,

you can issue the command, with a -Z flag, which stands for Zero Input/Output Mode.

A -V flag, which stands for Verbose, is also useful in this scenario.

This makes the commands output useful to human eyes

as opposed to non-verbose output, which is best for usage in scripts.

Side note, verbose basically means talking too much.

So, while I bet you want to throw up a flag on me and my jabbering,

we still have lots to get through.

Okay, so by issuing the Netcat command with the -Z and

-V flags, the command's output will simply tell you

if a connection to the port in question is possible or not.

On Windows,

Test-NetConnection is a command with some of the similar functionality.

If you run Test-NetConnection with only a host specified,

it will default to using an ICMP echo request, much like the program ping.

But, it will display way more data,

including the data link layer protocol being used.

When you issue Test-NetConnection with the -port flag,

you can ask it to test connectivity to a specific port.

It's important to call out that both Netcat and Test-NetConnection

are way more powerful than the brief port connectivity examples we've covered here.

In fact, they're such complex tools that covering all of their

functionality would be too much for one video.

You should read up about all of the other things these super powerful tools can do.

We've provided a few in the supplementary readings.

And after you've had a chance to read through the material,

we'll give you a short quiz.

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