Port Numbers Explained | Cisco CCNA 200-301

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In the last video, we looked at the layer 4 protocols TCP and UDP. Layer 4 is also responsible for choosing port numbers.

So why do we need port numbers? The example I give here is the postal service. To get post, you install a letterbox (at least here in the UK). This letterbox allows the postal service to access your home.

Network applications work in the same way. If you want to communicate over a network, you must allow some means of access to your device.

Let's say we want to access a web server. We type in the web address (also known as a URL) of the site we want to visit.

The first thing the computer does it convert that URL to an IP address.
This is done by using DNS, but we will cover than in another video. For now, just know it coverts web addresses to IP addresses.

The computer then sends the request to the webserver. The server will then look at the destination port to find out which application to send this data to. It can do this because there is a standard that port numbers follow.

When we made our web request, our computer knew we were trying to access a HTTP site. So it added the destination port number 80 to the TCP header.

The computer will also choose a randomly generated source port to receive reply’s on.

Several port numbers are called well-known ports. These are common protocols that have been assigned port numbers.
Examples of well-known port numbers are HTTP(80), HTTPS(443), SMTP (25).

0 – 1023: Well-known port numbers.
1024 – 49151: Registered ports that companies have registered IANA
49152-65535: Dynamic ports

Resources:

#ccna #cisco #networking

[orjihvy]

Wow, I don’t know why others can’t explain this basic idea clearly. Thank you.

[dandele]

Letting you know that I passed my CCNA 200-301 this week and your videos helped me do it! Thank you!

[christinalahey]

Thank you! My teacher has made port numbers sound like something that one can only understand with multiple doctorates

[bwood]

Thanks!
Everyone else only explained how ports are used without getting into what they actually are or how they operate which made it a lot harder to really wrap my head around them.
You provided a really great balance of explaining that without getting overly complicated.

[thelowertimeframes]

Yes! Port numbers, came at a a great time. If you guys would make a video on Cryptography or Encryption, it would be too great!

[berbid]

Never heard this simple yet comprehensive explanation in any of my computer classes in university.
Thanks for this great video

[fudoshin]

THANK YOU SO MUCH!!!! I was struggling with Ports but you just explained it so easily. Thanks again 🙏 💕

[Malitubee]

Bro literally why can’t anyone else just explain it just as easy as you did ! You made this click instantly, it felt like everyone else was speaking a completely different language

[Randumb]

These videos have really helped me wrap my head around so many networking concepts

[rishithilak]

sir you are the perfect teacher ever i have seen you giving an every real time example for each topic this makes me practically strong.loved your teaching

[MathoAvito]

Thank you so much for the great explanation!
The best sentence in this video was "IP address gets the data to the computer, but it's the port number that gets the right application"
Wrote it down for myself.

[tokinabo]

wow, a clear nice voice, at digestible pace, with in depth detailed and yet simple explanation!
hard to come across those days..

[JoseRuiz-mfzb]

This video made my life so much easier, I just spent a whole semester of just reading and reading and reading, and I literally learned more in this video than the whole semester

[moneymaker]

Best video for this concept in the whole you guys❤️

[thatguyluffy]

Crystal clear on the basics ! good explanation with the figures

[conorbase]

This is a really informative and fruitful video. I nearly took notes for every sentence in the video.

[denisewray]

Thank you, your video took the confusion out of understanding what Ports are and how they work.

[mehdiroudeau]

i am from france and I still understand your explanation better than my own teacher thanks a lot m8

[mofojackson]

Just saw your excellent video explaining TCP UDP and was going to ask if there was one on ports when this auto played haha. Awesome and exactly what I was wanting to know next

[leggeddog]

I've been in IT for 20 years and I still learned something from this.
Never did get my ccna certificate, i just had to learn as I went after college