The OSI Model - Explained by Example

[@hnasr]

Hey guys in minute 16:00 I forgot to mention this is a WIFI configuration not wired . so all devices within range will receive the those packets since they are in radio vicinity and drop them if they are not intended for them. if that was wired than the router (acting like a switch) will be smart enough to only forward to required device by identifying which port it is connected to.

[@EngineeringEspy]

I was really confused until i saw this comment. Thanks! However, I do have a question, in a network of only wired computers, how could someone listen for packets? If the router is only sending the packets to the intended recipients, then I don’t see how someone could sniff packets unless they had access to that router. Basically, would tcpdump or wireshark work in a completely wired network?

[@asimarunava]

Yup. At 16:00 i paused the video came to comments section.

[@mbesida]

in case of wifi, doesn't the client set the destination as a router(which is a default gateway for it) at some layer and then the router directs the packages to the server? So, basically, the server receives the package twice: first time from the client and second time from the router; but first package it drops at some lower layer as it doesn't know yet that it is the destination of that packag. Or in case of wifi, the router even doesn't takes a place in client-server communication? Why I'm asking, becasue at the moment when client sets the destination at data link layer it doesn't know what media will be used to transfer the data(wifi or wired connection) so it sets as a address its gateway

[@YugankSingh]

that's what is was wondering shouldn't router/switch do it for you

[@nikhilramabhadra6052]

Great video.

[@Ryfibi]

I feel like I want to quit my job and spend a few weeks just studying your backend topic videos. Really interesting stuff. I was even able to explain to my wife why she can't access homebanking in a starbucks.

[@dicksonchibuzor2792]

Same way I feel!! So sad I discovered Hussien late!

[@pabloeterico]

I quitted my job and and I discovered this channel... I know that feeling, i think I need at least one month to watch all the videos and after that maaybe get another job 😆

[@kehindejacobmetibemu9193]

@@dicksonchibuzor2792 seriously

[@syedshahzaibzafar2422]

exactly. I was also thinking to take a break from my job to deep dive into backend.

[@tau_hacking]

i am also doing it

[@hnasr]

Guys here are some jump codes to help you navigate, 2:15 public vs private ip address, 4:00 Application Layer, 5:30 Presentation Layer, 6:20 Session Layer, 7:20 Transport Layer, 9:20 Network Layer, 11:20 Data Link, 13:00 ARP protocol, 14:00 Physical Layer, 19:00 Why you shouldn’t connect to public WIFI I enjoyed making this video!

[@yohannesg.medhin687]

I have a lot of question. Would you help me?

[@unknown-bx8my]

Thank you for this great tutoriol❤

[@palaniappanrm6277]

"Intended for you as a device, but not as an application" - Perfect way to explain the way the router works when you make a request to external network 👌

[@andrescastillo2863]

Summary of: OSI (Open Systems Interconnect) model, from a software Engineer's view (Please correct me if I'm wrong): Layer 1 Physical This is the physical layer, in which 1 and 0 data bytes can be sent as electric signals, wifi, or light via "the wire" Layer 2 Data Link These are the separation of the data bytes into frames. Notably, the frames will identify the source and destination MAC addresses of the devices' network card. Since electrical signals travel in all directions in a network, the data frames reach all devices in the network. Once the data frame is able to identify that the device is not the intended destination, the frames drop. In an unsecured network, this is where a malicious application can choose to not drop the frames, and steal the data. Layer 3 Network Once layer 2 is done, it generalizes the frames from MAC addresses to IP addresses. Layer 4 Transport This tranport layer further generalizes the network layer IP address into source and destination ports. Layer 5 Session Since there may be several TCP connections to one server at a time, with identical packet information from layers 1 through 4, we need a way to distinguish the session by ID to tag it. Layer 6 Presentation This is where the resource might be secured/encrypted with HTTPS/TLS by scrambling the HTTP request string. I didn't know HTTPS encrypted anything. I thought it was only a way to identify the true identity of a website. Also, encryption might be accomplished via VPN. At this step, if the data is encrypted, the model decrypts the information to reach step 7. It might be possible that a malicious attack to steal data can be avoided by encrypting. "This is where you can get screwed if you are on public wifi...people can sniff your data." Layer 7 Application This is where a client device makes a request to a server device, such as a GET request. This request contains a whole bunch of information, such as headers, cookies, content-type headers, etc, which is summarized into a string, so the string can participate with the rest of the OSI models as byte data.

[@hnasr]

Andres! Amazing summary thanks for taking the time to compile this. It would be nice to separate the summary based on the sender vs the receiver . Thanks for being a fan of this channel :)

[@praiseokonta8879]

Damn. Nice one. 👍Anyway you could summarize quantum mechanics too?

[@Aman-lo3jb]

@@praiseokonta8879 😂

[@kenwu7]

@@praiseokonta8879 Lol 😂

[@kenwu7]

Read this after watching. Great summary to recap everything 👏👏👏👍

[@AbandonedVoid]

It is a dry topic, but somehow even with your thick accent and minimalist presentation style, your charisma makes this video a joy to watch. Seriously.

[@cppdog3549]

Hi Hussein, thank you for making this video. I just want to clarify one thing. At 16:20, you say that the stream of bits that are being sent from the client will go into server 1,2,3,4..etc essentially to all servers. This is not correct. I'm a software engineer working in networking domain, and in networking the direction of packets is either "unicast" (meaning it's directed to one client only), multicast (meaning it's directed to two or more known clients), or broadcast (meaning the traffic is directed to any machine that's on that network). In your case, since the server is hosted on machine C, the data is directed to that machine and it will only go to the router first and then to that machine regardless of the medium used to transfer the packet (Ethernet or WiFi). If the stream of bytes were transferred using WiFi, you are right in that the data will be broadcasted all over the place using radio waves but only the router will be able to interpret those packets, because that's how WiFi works, and the other machines (even if they have a WiFi receiver) will not be able to decode the packet and see the bit streams. Just wanted to point this out to clear any confusion. Thanks for making these video. They're very useful and informative.

[@pfteve]

I looked in the comments specifically for this

[@devarsdk]

but how does physical layer know that the server is hosted on C ? How does it decide to route to C at physical level ?

[@amiralam1786]

@@devarsdk the physical layers knows that this is for him, and he then checks to what local ip he needs to redirects it request and then it broadcast the wave again and that;s for C

[@hashcoeur]

Hi, this context helped me a lot. Sometimes I see the term anycast, has something to do with this. Is it the equivalent to broadcast?

[@saimirfan902]

@@devarsdk You need to learn about ARP protocol. I think that will solve your problem

[@Deepakkumar431]

Your Channel is a gem. I landed on this channel searching about the difference between proxy vs reverse proxy, ended up watching at least 10 videos as of now. Though I am a frontend engineer, still I feel everyone should have this basic networking knowledge.

[@hnasr]

❤️ thank you Deepak! Welcome to the channel

[@saahilnayyer6865]

First ever I came across the concept of OSI was in 3rd year bachelors and it's been 4 years since. Today is the first time I can say that I understand the whole damn thing and what each layer does. You are a legend Hussein.😁

[@jeffreypham5687]

I have watched many youtube videos on the OSI layers, and this is my favorite one. This really gave me a good understanding of the OSI layers in a real world scenario. Explained simply and gets the points across. Just great!

[@hulk94smash]

Omggg where was Nasser in 2015 when I was pursuing my undergrad?! Computer Networks made me cry as a subject just because I could not digest the huge amount of information bombarded at us during the coursework. This info along with the diagrams, is gold 💯. Really helped me understand the OSI model - something I thought would never be possible (coz I tend to get lazy when things stop making sense or when I'm unable to visualize what is happening)!!! Thank you Nasser 💯❤

[@sarveshrawat1462]

Congratulations!! Your content has reached India. Now, sit back and watch your channel grow.

[@pratikgaur21]

Your humour lines in between your awesome teachings are really nice and engaging. Thanks for a refresher and keep it up!

[@ebymathew8578]

At last i laughed when the web server got the GET request😉😉😉........Awesome explanation

[@crazycat664]

Bro you just made the most boring CN topic the most interesting one. Hats off to you brother, keep up the good work.

[@shubhamchandramishra636]

I wish i could understood the Beauty of OSI model a year before. Really awesome video ...

[@shreyasmali3566]

I don't think I've ever heard any explanation of any topic to be this much interesting and fun ever! Thanks a lot! I wish I could learn every other subject from you...

[@varaprasadhalajangi8200]

i just addicted to this channel.

[@MrHellRock]

A huuuuuuuuge plus from me. This is a best explanation of network communication I have ever seen in my engineer career.

[@vishalvatsalya1439]

I am binge watching the backend engineering playlists. Awesome content. Keep up the good work! :)

[@hnasr]

Enjoy!

[@lakshayasood2197]

thank you sir.. you just explained something in a great and easy way that i couldn't understand though out my computer networks class. Now i am less scared of the subject

[@hnasr]

Lakshaya Sood really happy I could help! Best of luck on your study 📖 cheers!

[@felipemartinezalbeche719]

Hey Hussein! You really rocks!! It's amazing how clearly your explanations are about complex stuff! Congrats!

[@harshitanand7349]

So now I can explain to non-techie people why you shouldn't connect to a public wifi network!! Great video 💯

[@karthiksatish9030]

very very very underrated video, The best explanation I have ever seen on youtube sir.Thank you for making these kinds of videos 🙏🙏🙏🙏🙏🙏

[@mohammedyoutube6102]

I have used Wireshark before, and the way you introduce it in the video makes me try to correlate every technology that I am using as a developer.

[@markbenjamin1819]

Literally after going through the video I felt like I have achieved a lot today already. Thanks you.

[@محمّد.09]

This was hugely helpful for me to get into cybersecurity.

[@peppermintdior]

I am soo glad i found your channel right before my Amazon interview ♥

[@shrirangdiwakar]

My god!! I’ve been trying to understand OSI from so long but theory sucks!! Glad that i just found your video! First time i got entire thing cleared ! Great work

[@tobiowolawi5044]

the best explanation about how packet sniffing and interception works. thanks for this!

[@LLDG]

I have been listening to your videos for days. I can finally understand this stuff. Thank you so much!

[@hnasr]

❤️❤️❤️

[@simoghf1888]

Sir, you make evrything seems as simple as the waterflow , thank you so much for all of your efforts

[@gulnarismayilzadeh8791]

Thank you for this great explanation. After 8years finally I understood this model.

[@aniketverma7786]

The best video ever made to explain OSI

[@hnasr]

Thank you Aniket!

[@MamboslilMicroscope]

I am Definitley going to use this approach to explain the concept to people

[@pavansrinivas4388]

Hey Nasser, This is the best explanation I have seen for OSI model. Thanks for the great video.

[@hulk94smash]

The "Yayy" at 4:58 had me weak 😂😂. Love your content man.. you give direction to aspiring backend engineers. Please make more 💯

[@DarkRevan36]

This video gave me a great understanding of the OSI and is a fundamental part of my progress in IT! Great work!!

[@jahedulislam3438]

A gem in tech world. Gracias brother.

[@navkanttyagi5376]

ohh god i am so happy i found ur vidoes and so excited to watch all ur videos......i swear i am gonna binge watch ur videos.....and thanks a lot to you for making such amazing videos........sending lots of love to you.......thanks man

[@hnasr]

Sending love ❤️ back

[@acalabash]

Best explanation of OSI I've ever seen (and I've seen lots of them)

[@Apoorvpandey]

"I was in university 10 .... Ohh no maybe 20 years ago ... Damn I'm old" 😂😂😂 But you make awesome tutorials ... Keep it up !

[@hnasr]

Apoorv pandey 😂 Thanks 🙏 glad you enjoying the content

[@unknown-bx8my]

😂😂😂😂

[@greatcoolthings]

Thank you for the explanation Hussein! I was first exposed to the OSI layer through work when dealing with CAN networks in industrial vehicles (EE background), and have never found a resource that would help me create a solid mental model until now. This is it. The example is great, and it explains OSI's layers and main concepts really well.

[@IktaSol]

" OSI is Open Systems Interconnect, I don't expect you to remember it" Me: "meh I think I will" *midway through the video* "what's OSI again"

[@jitpackjoyride]

I relate too much to this 😂😂

[@xsorn]

This is explained really well and it is abstraction done right for beginners. Good job and thank you!

[@hnasr]

Thanks! Glad you enjoyed the video cheers!

[@SuperOnlyP]

19:00 Now it makes sense why people try to use Wireshark to capture data in public wifi network. thanks !

[@DeepakSingh-hl3er]

Finally i managed to understood OSI. Thanks Nasser.

[@sojourningstudios738]

Very useful, entertaining description of the OSI Model. Now I understand more about why it’s important to encrypt data in transit.

[@kelvinmburu2698]

Thank you man for this. I wish you know how long i have been stuck in the osi plateau. It just clicked

[@abdelbassetchettouh7416]

@hnasr I've been always seeing osi model from bottom(network engineer view) Now that I'm seeing it from top( software engineer view) a lot of stuff becomes more clear. Great work brother, keep up the hard work😊❤

[@mahdizarepoor8964]

You are just great . the way you explain and keeping things as simple as possible make your tutorials so interesting .

[@searchapostateprophetabdul2398]

People like you are who actually run this world 😔

[@nocprojectuser9674]

Packet in Layer 3 encapsulate in Layer 2 frame by adding source MAC address and destination MAC address(in case of Ethernet) and add some FrameCheckSequense. Hussein, in your explanation 2 packets of network layer divided into 3 frames of data-link layer, I think its not true. If IP destination in same LAN with source, Then destination MAC equals MAC of destination host, in other cases Destination MAC will be MAC of host with IP equals default gateway, this mac will be known by ARP request about IP of host in same LAN or IP of default GW. Maybe this is an unnecessary explanation for a software engineer, but in fairness I wanted to write about it. Thank you for good content.

[@ayushtripathi2895]

Finally found the perfect video after searching for long. Thanks!

[@erensrtky]

Thanks for another good explanation bro, as a web developer your videos help me lot because they are basic and very understandable.

[@hnasr]

Eren Sertkaya thanks Eren, happy I can help and we all have room to always learn more! Its an infinite field

[@kubic22562]

Very well explained if it comes to particular layers, what happens in every layer, however the last part of video seems to be a bit too oversimplified for me. I think you should exemplify how data travels from one device to another with more 'tricky' network topology. Also I think you should distinct network devices such as switch, router and firewall, because in fact standard SOHO (small-office-home--office) 'router' consist of those 3 devices combined into one box. Of course then the video wouldn't last 25 minutes, this is knowledge that need some time to be explained :) Anyway, I love your content, your channel is really good place for backend engineers. Greets from Poland!

[@krisspringer7869]

I love this guys accent. Sounds like Shrek is giving a tech training. It's awesome and hilarious

[@rubixtheslime]

Wow I never even noticed. I kinda thought he resembled the Indian guys with hypercam2 from 2008. Which is a good legacy to hold up to.

[@fahad_mihran2286]

I am able get this since I am from networking background. don't know if begineers would get this. But good content for people with background

[@biprajeetpal]

I never really understood this in college too and now I do. Thank you!! :)

[@ThamaraiselvamT]

Electricity does not have a direction (Omg) I learned something new today. Thanks for your video. you really helped me to understand OSI model finally :D

[@satyajitkamble1646]

Best OSI explanation ever!

[@mohammadahmedragab837]

thank you so much, you amazingly simplified a complex topic that I did not fully understand when I was in university ❤️❤️❤️

[@naveenkumarch5991]

Thanks Hussein! These videos are brilliant. I wish I had discovered them earlier.

[@hnasr]

No worries! glad they are helpful!

[@chahatqureshi6094]

no I am not yawning, its interesting how you are giving related knowledge also with the topic information. keep it up this way, i like it thank you for this informativve vedio.

[@khammassihoussemeddine1193]

i'am proud of you Hussein u r a pride for all the Arabic and Muslim world

[@Edekje]

Dear Hussein, awesome video. I learned a lot and loved and laughed with every bit of your explanation!

[@princeomonuitanyi6449]

The part about "electricity has no direction" is so cool 🤭

[@sairam-lj6zu]

Superb video Hussein. Could you please elaborate on session layer ? If that is unique then why can't we use it as a session identifier which is more secure than the JSESSIONID etc., Also HTTP is stateless right, how does this session layer makes any difference ?

[@gangstaberry2496]

Very practical examples, excellent as always

[@singaravelann3671]

Hi Hussain Thanks for making such a wonderful video on most confusing topic ever, Now I understand how does this OSI model works on higher level, Can you also please explain how does three way handshake work's on context with OSI model, And how does it maintain the session between client and server in context of OSI model.

[@hnasr]

Thanks! Yeah thats a great topic! I haven’t discussed on my channel

[@singaravelann3671]

@@hnasr Am really waiting to see that video , thanks a lot for all your effort am really enjoying it.

[@quianahastick8939]

literally the best explanation fr

[@bhang96]

Excellent explanation even compared to the university course. Thanks so much and all the best Hussein.

[@porchezhiyanelanthirayan1816]

Thank you i wish i found your channel much eariler...

[@hnasr]

Thanks ! Your here now and thats what matter. enjoy the content ! And tell me what should I make next .

[@ZzBiazZ]

Thank you so much for doing this, I have watched a lot of your video :3

[@hnasr]

Great! Thanks for your comments very happy I could help. Let me know what other software engineering content you would like me to make 😊

[@pathshala9075]

You are just insane buddy....amazing.....thank you millions

[@namazbekbekarysuly9112]

Gosh, brilliant deliver of dry OSI theory. Thanks!

[@HimanshuKanodia]

Thanks 😊 are you going to dig deeper in this topic?

[@shanibburney8290]

Loved your way of teaching Hussein Sir ❤️ Never stop what you're doing. You are great at it.

[@hnasr]

Thank you 🙏

[@vijayredkar6680]

@Hussein absolutely nice explanation. The thing about bits converting to light is an eye opener. Just makes it so clear to connect the dots now. Thanks buddy!

[@vivekatbitm]

Thanks for yet another awesome video. Have two questions, if you may answer: 1. U said webserver can have at max 7 session, but that depends on server, isn't it. A server can handle multiple TCP connections. 2. As data goes to all devices, even to device it's not intended to, how does data download counted. I mean which layer handles what data should be counted as download to avoid reaching data download limit because of unintended data.

[@hnasr]

Hey thanks! 1) hmm I don’t remember saying that, if I did that is not correct. Can you point me to the timestamp in the video? 2) the device layer 2 filter it out by looking at the frame mac address. Obviously you can build a device that ignores that and actually receives all packets in a wifi network.. thats why its important to encrypt

[@vivekatbitm]

@@hnasr thanks Nasser for instant reply. 1. Check at 22:34 onwards 2. My question was if all data is received by all devices, all such data will be counted as download and will eatup data limit provided by ISP. There must be someone who count only intended data as user's own data. Which layer does this? Hope I made my question clear this time.

[@hnasr]

Oh the download portion is not really true because this data is coming from another interface of the router. The download qouta will only be counted when stuff comes from ISP down to the router.. check out this video kzbin.info/www/bejne/bIXJaWOjl82sd7M

[@sanskarkaazi3830]

"Took me 12 minutes to figure out the animation" - Lowkey flex by Hussein, the BackEnd engineer lol.

[@mohammedrehaan2811]

Good stuff man finally demystified for a dumbo like me

[@jasondinh5603]

Dude, this is GOLD.

[@anamkhan1941]

it really is cool to finally understand what's happening. thanks a ton!

[@theSeniorSDE]

Thanks a lot Hussein for sharing this. This is really amazing and the way you have explained is so awesome.

[@sunguru981]

Hey Hussein. Thank you so so much for this wonderful lecture. I feel like something has been unlocked inside my brain haha. A quick question regarding this transmission of data between internal servers. You have demonstrated the network travel from a device C to device D, all connected to a private router. Could you please say in short what happens when I connect an external ip of a server from one of my devices, like say for example 237.65.42.121 is some external ip and Im connecting there. What would happen at that point regarding the public wifi? Im asking this question because now the destination device is not within the public wifi connected devices and is somewhere at the other side of the world. At this point how would the other guys were able to see the data. Again Im a bit confused as the example was solely relied towards a LAN and not a WAN. Apologies for this long message and thank you so much once again. I started my career as a full stack dev 3 years back but never knew there existed such depth in backend. I just started watching your backend engineering playlist and its so so fun to learn all these nuances behind. Feels so satisfying haha.

[@hnasr]

Thank you Sundeep for your comment! Glad you enjoyed the video and found it helpful. As for your question, I believe you will like this detailed video on what happens when you go to google.com kzbin.info/www/bejne/mpmXYWmFZ9uSZ8U

[@sunguru981]

@@hnasr Tons of thanks for that redirect. Let me summarize what I learnt from the video. If the connection is between a LAN network, (10.0.0.1 to 10.0.0.5) then it just goes directly to it, by asking each device "hey are you 10.0.0.5?". But if that is a WAN network, then our router would be the medium (gateway), between us 10.0.0.1 turned to some external IP of 44.3.28.12 and the external server of IP 237.65.42.121 Now the crux of my understanding is, while we are going through the router, that is the reason the other connected devices still know what we are asking, coz now we are technically still bound with our router's IP. Please correct me if I am wrong. I am a bit noobie in this department, but Im trying to learn haha.

[@elijahlair]

I really enjoyed watching this, brilliant explanation. Thanks❤

[@vishalrajput4402]

Really a great understanding i have got today😇

[@solmazk7418]

Great explanation! I'd also like to learn what happens to the response to that GET request and how does it work when the request is for a device outside of this network(going through DNS ...)

[@hnasr]

You will like this, I go through details what happens when you go to google.com kzbin.info/www/bejne/mpmXYWmFZ9uSZ8U

[@solmazk7418]

@@hnasr I tried watching it once, but it felt too advanced. I'll try again! Thanks

[@betolix]

Hey Hussein, Your videos are very didactic and helpful, thanks for that. However layer 2 (switches ) breaks the domain of collision of a datagram. In the picture what looks like a router includes a switch capability and therefor a datagram would not broadcast to all the devices in it’s network. Please let me know if I miss understood your explanation. Thanks again.

[@hnasr]

Thanks Alberto you are absolutely correct. The router (switch to be exact) will route datagrams to the specific mac addresses based on the port. I am not sure how this works in WIFI/4G,

[@soufianta8374]

Nice comment because I was a bit confused about the fact that every data is send to everybody all the time. Switches and routers doesn’t make sens if I follow your explanation but thanks to discuss it in the comments. Broadcast data will arrive to everybody.

[@shovonbasak7008]

Thank you sir. Really enjoyed this journey of data. ❤

[@hnasr]

Thanks Shovon! Its impressive right? Seeing how data flow

[@thekreempuff]

Such a good video overview of the topic. Great illustrations and presentation

[@mashawin4796]

You technology video is awesome. I'm additiction of your video... Could you please make one seperate video for TCP and UDP header explaining piece by piece if possible...

[@hnasr]

Nice suggestion! Tcp vs udp is definitely on my list

[@hnasr]

Masha Win tcp vs udp kzbin.info/www/bejne/p6K1ip6ZqcZpf6c

[@akumasdeception]

Thank you for making this so simple to understand!

[@AndrewReeman_RemD]

This video is great. Clear explanations. Thanks for making it 👍👍

[@techwithameer]

What's all going behind a simple request?. Amazing

[@coolbuddy2405]

Thank you for explaining so well. Thank you for your efforts

[@yusufmirkar6508]

I was always confused what is the use of session later, when we have transport layer which has connection info. Just understood session identifier is created at session layer, so connection is actually created at session later where session is assigned to connection. This is what I understood. 2nd point i understood in this video is use of presentation layer - which is ssl/tls in case of https apart from many other uses possibly

[@khalidamer7305]

Thanks for this amazing video, How does the destination device decrypt?

[@lorenzop.8249]

fucking hell this is the best explaination on the topic... amazing