Module 2.3a IP 0:00 - 1:00 -

Transcription

1 Module 2.3a IP 0:00 - In this video we're going to continue looking at our simplified view of how the internet layers work and in particular we're going to look at the middle layer which is good known as TCP/IP. Before we get too far into this I wanted to remind us of one of the core concepts of using this layer model, and if you recall we talked about a voice conversation message where the top two layers were the same as a postcard communication message. So I want to emphasize is that the higher layers can communicate without any regard as what's happening at the lower layers and that's really important with our model and how we construct messages and send them back and forth. So we're talking about our middle layer of TCP/IP it doesn't matter if the lower layer is working over Wi-Fi or ethernet or cellular connection it doesn't matter, everything we're going to say now moving forward does not have to be concerned with how that physical layer is actually used. So let's take a look at how the middle layer TCP/IP actually works now I 1:00 - mentioned we're giving a simplified view the TCP/IP layer is actually two separate layers, the TCP layer which is a higher layer than the IP layer but for all intensive purposes we're going to consider them the same layer just for simplification. Now full disclosure there is an alternative to TCP that is used in the real world known as UDP or user Datagram protocol. We're not going to really discuss that but I just want to make sure for full disclosure aware that some of the

2 technologies that you use do not use TCP although the vast majority of communication you use on the internet is actually TCP. So the first thing we're going to do is describe IP or the internet protocol, and that's literally what the internet is named after this IP Internet Protocol. In order to send a postcard in the real world you need a destination address and usually you have a return address that you sent it from. Well, you need both of these to communicate on the Internet, and to communicate on the Internet you need the same sort of idea. This protocol requires that you have a sending address where it's coming from and you need a destination address of 2:00 - where it's going to. Now this address does not look like our normal addresses we use for mailing addresses, they use the specific scheme to keep track of all the different devices on the internet. So what is an IP address look like. Well it's four numbers, each number is in the range from 0 to 255. So there's 256 possible numbers. Then you string them together separated by period. Currently is really the number If you launch your browser and you just type in up comes the University of Waterloo. Now that's not very convenient. We ll talk about a different way of addressing website soon but that is an example of how each computer or device on the Internet has its own IP address. Now unfortunately we are running out of IP addresses. If you count up the total number of devices that can be on the internet is 256 x 256 3: x 256, which is approximately four billion different devices. When the internet was first being conceived of, that seemed like a perfectly valid number of IP addresses but when we enter a world where each one of you may have multiple devices and there's lots of hardware that connects all of the internet we have run and we're past four billion devices. So they had to come up with a plan B. There's two ways to address this problem. The first is what they call IP version 6, and the idea of an IP version 6 is that you have a much longer IP address. This is the actual IP address of another computer at the University of waterloo, that uses the IP version 6 scheme. With the IP version 6 scheme we can handle 340 trillion trillion trillion devices on the internet. And that should serve humankind for a long time. The alternative scheme is called Nat. So you did not type in into your web browser, you can just type in So what happens is there is a

3 4:00 - protocol named DNS for Domain Name System. And what happens is when you type in your computer sends that request out to your local DNS server and it then returns back the actual IP address of what you're trying to connect to. So it converts between a more user-friendly human name to an actual IP address. Now your local DNS server may not know exactly where uwaterloo.ca is, so it may go on to say for example the.ca DNS server and says hey you're in Canada do you know where this address is and then it may have come back with the number. So it may require more than one hop to a different DNS server but eventually no matter what name you type in it will come back. There is an international body out there that decides who can get what name. You cannot just go ahead and say hey can I be microsoft.com. So what happens is you can register different names and you can go out and register names for yourself so 5:00 you can have your own custom or vanity name or if you have a business you want to start up you can get your own name. And then you what you do is you register that with an agency that associates your name with a real-world physical address. This is a controversial topic there are countries that control their own rules for how you can get a name. So for example if you want to.ca within Canada. And then there's other new top-level domains such as.ca,.edu,.org and each of these have their own rules for how you can obtain your own name. At the end of the day though you don't have to worry about this, you just simply type in a name and your DNS server will resolve that to an IP address. Now I mentioned that there's only four billion IP addresses out there

4 6:00 - how do you get an IP address. Well there's two categories of IP addresses, there is fixed IP addresses, and big companies like Google and Microsoft have their own fixed IP addresses as well as organizations like the University of Waterloo. In fact, every number that starts with is an actual University of Waterloo address. University of Waterloo has that entire range. But you're just a regular citizen and you want to connect to network whether you're at Waterloo or Starbucks or at your home network. And each one of your device's needs an IP address. Well the way these on the fly or temporary IP addresses are doled out, is known as DHCP, which stands for Dynamic Host Configuration Protocol. So the idea is your device when it turns on and it tries to connect to a network it's sort of sends a message out hey I don't have an IP address can I have IP address please, and then what happens is there's a DHCP server out there that has a bank of IP 7:00 - addresses that it can give out. And what it will do is, it will give you an IP address that you can use. And it also will expire after a certain amount of time, so if you go to Starbucks and Starbucks gives you an IP address that's great but an hour later when you're gone someone else can get that same IP address. And so the DHCP server just keeps track of addresses it has available and gives them out as needed. This is especially important for your mobile devices like your phone and laptop where you may connect to multiple different networks. Now the last tricky piece I want to explain which will really help your understanding of how communication on the internet works, is known as Network Address Translation, and when you connect to your home network or even Starbucks or places on the campus this system is used so that we don't run out of IP addresses. So how NAT actually works is a little complicated, and I don't want to get bogged down in details, so what I'm going to do is give you an analogy using physical addresses that will just give you an understanding of how basically it works. So let's say we have an apartment building and that

5 8:00 - apartment building has a physical address known as 555 real street. That's a real physical address in our world but there's a whole bunch of people who live inside the apartment building and they don't even know they're at 55 real street. They all think they live at imaginary lane. So one person might think they live at 100 imaginary lane and someone else might live at a hundred and one imaginary lane. So you might think you live at a hundred and one imaginary lane and then you want to send a postcard to your friend who lives at destination avenue. So you fill out your postcard dear Bob at 789 destination avenue and you return address you put as a hundred and one imaginary lane. And then what you do is you hand your postcard to the nice doorman who lives at real street 55 real street. So you say hey doorman can you please deliver this postcard for me. He says no problem, and then what he does is he changes your return address to be 55 real street, unbeknownst to you. And then he sends out the postcards the destination avenue and then your friend at destination avenue 9:00 - gets your postcard sees your address is 555 real street and then sends it back to you. And then when it arrives the doorman looks at your postcard and goes A HA this is my friend who lives at a hundred one imaginary lane, and again changes the address from real street back to 100 imaginary lane and then passes the postcard onto you. You were completely oblivious to this whole thing the doorman was doing all of this managing for you. So what happens is we can have hundreds or even thousands of computers all sharing the same physical address, and this is another way of getting around this problem of running out of IP addresses. So when you go on your computer and you ask your computer hey what s my IP address, it might come up with a number such as imaginary lane. And in fact, if your IP address begins with , you live in imaginary lane. Alright we just discussed a few technical issues that help us understand how the internet works and how the internet protocol works, but let's actually talk about Internet routing because that's one of the core parts of

6 10:00 - the IP protocol. Whenever your computer sends out a message it has a destination IP address and your computer sends that to a local router and that router may send it to another router, and then another router and eventually you'll reach the computer that it wants to reach. All of these individual routers are all connected together and are constantly sending millions of messages back and forth back and forth and that's how your message gets from one side of the world to another side of the world. How does this work? Let's discuss how it works in the real world say you live in Kitchener Waterloo, and you want to send your postcard to someone in England. Well you fill out your postcard and you get someone's address in England and then you take it to your local mailbox. And then someone picks up that postcard from the mailbox it takes it to a central depot, and they look at the address and they say oh this one's going to England so I might send that to the central Ontario dispatch, I don't know how it actually works in the real world I'm making this up. But we can imagine that it goes to a central Ontario dispatch and someone looks at the address there and goes all this 11:00 - is going to England. So they take it to a candidate dispatch center and then at the candidate dispatch center they look at this address and go all this is going to England, well let's put it on this boat that travels to England and it goes over the sea, on some sort of big boat and he gets over to England and then someone opens it up and goes ahh ok well you want to go to London England, so let's put it and let's give it off to someone who delivers in that region. And then eventually you'll get narrow and narrow and smaller and eventually it will show up at someone's house. So this idea of each person who looks at the postcard along the way knows in general which direction the postcard has to go. And it's complicated but that's how all the network routers on the internet work. Whenever you send out a message each one of them send it to another router that will get you closer and

7 closer to your destination. Now it's hard to visualize how all the routers in the world are connected, I stole this photo and this is from 1999 so this is even a long time 12:00 - ago but this is a visualization of many of the routers that exist in the real world. And so you can see how you might start in one corner of this giant network and make your way through a whole bunch of different paths to your destination at the other side of the world. In general, every message you sent on the internet takes less than 50 hops and a hop being, goes from one router to another router. That's still a lot but you can reach almost any computer from any other computer in the world within about 50 hops. And that's how all the messages on the internet get transmitted. Raw Long Form Transcript 0:00 - in this video we're going to continue 0:02 - looking at our simplified view of how 0:04 - the internet layers work and in 0:06 - particular we're going to look at the 0:07 - middle layer which is good known as 0:10 - tcp/ip before we get too far into this i

8 0:13 - want to remind us of one of the core 0:15 - concepts so using this layer model and 0:17 - if you recall we talked about a voice 0:19 - conversation message where the top two 0:22 - layers were the same as a postcard 0:24 - communication message so i want to 0:27 - emphasize is that the higher layers can 0:29 - communicate without any regard as what's 0:31 - happening at the lower layers and that's 0:33 - really important with our model and how 0:35 - we construct messages and send them back 0:37 - and forth so we're talking about our 0:39 - middle layer of tcp/ip it doesn't matter 0:42 - if the lower layer is working over Wi-Fi 0:45 - or ethernet or cellular connection it 0:47 - doesn't matter everything we're going to 0:49 - say now moving forward 0:51 - does not have to be concerned with how 0:52 - that physical layer is actually used so 0:55 - let's take a look at how the middle 0:57 - layer tcp/ip actually works now i 1:00 - mentioned we're giving a simplified view 1:02 - the tcp IP layer is actually two 1:04 - separate layers the TCP layer which is a 1:06 - higher layer than the IP layer but for 1:09 - all intensive purposes we're going to 1:10 - consider them the same layer just for 1:12 - simplification now full disclosure there 1:15 - is an alternative to tcp that is used in 1:17 - the real world known as UDP or user 1:19 - Datagram protocol we're not going to 1:21 - really discuss that but I just want to 1:23 - make sure for full disclosure aware that 1:25 - some of the technologies that you use do 1:27 - not use TCP although the vast majority 1:29 - of communication you use on the internet 1:31 - is actually tcp so the first thing we're 1:34 - going to do is describe IP or the 1:36 - internet protocol and that's literally 1:38 - what the internet is named after this IP 1:41 - Internet Protocol in order to send a 1:43 - postcard in the real world you need a 1:45 - destination address and usually you have 1:47 - a return address that you sent it from

9 1:49 - will you need both of these to 1:51 - communicate on the Internet and 1:52 - communicate on the Internet 1:53 - you need the same sort of idea this 1:55 - protocol requires that you have a 1:56 - sending address where it's coming from 1:58 - and you need a destination address of 2:00 - where it's going to now this address is 2:02 - not look like our normal addresses we 2:04 - use for mailing addresses they use the 2:05 - specific scheme to keep track of all the 2:08 - different devices on the inner 2:09 - they're so what is an IP address look 2:11 - like while it's four numbers each number 2:13 - is in the range from 0 to 255 so there's 2: possible numbers and then you string 2:18 - them together separated by. currently 2: burr 129 got 97. too late. 2:28-23 if you want your browser and you just 2:31 - type in up comes the 2:38 - University of Waterloo now that's not 2:40 - very convenient will talk about a 2:41 - different way of addressing web site 2:43 - soon but that is an example of how each 2:47 - computer or device on the Internet has 2:49 - its own IP address now unfortunately we 2:53 - are running out of IP addresses if you 2:55 - count up the total number of devices 2:57 - that can be on the internet is 256 x 256 3: x 256 which is approximately four 3:03 - billion different devices when the 3:05 - internet was first being conceived of 3:07 - that seemed like a perfectly valid 3:08 - number of IP addresses but when we enter 3:11 - a world where each one of you may have 3:13 - multiple devices and there's lots of 3:15 - hardware that connects all of the 3:17 - internet we have run and we're past four 3:19 - billion devices so they had to come up 3:21 - with a plan B there's two ways to 3:23 - address this problem the first is what 3:25 - they call IP version 6 and the idea of 3:28 - an IP version 6 is that you have a much

10 3:30 - longer IP address this is the actual IP 3:33 - address of another computer at the 3:34 - University of water leave that uses the 3:36 - IP version 6 ski with the IP version 6 3:39 - scheme we can handle 340 trillion 3:42 - trillion trillion devices on the 3:44 - internet and that should serve humankind 3:46 - for a long time the alternative scheme 3:49 - is called Nat 3:51 - so you did not type in :55-23 into your web browser you can just 3:58 - type in has there's a 4:02 - protocol named Dee and ask for domain 4:05 - name system and what happens is when you 4:08 - type in www waterloo your computer sends 4:12 - that request out to your local dns 4:14 - server and it then returns back the 4:17 - actual IP address 4:18 - of what you're trying to connect to sew 4:20 - it converts between a more user-friendly 4:22 - human name to an actual IP address now 4:26 - your local dns server may not know 4:28 - exactly where you water. CA is so it 4:31 - may go on to say for example the. see a 4:33 - dns server and says hey you're in canada 4:36 - do you know where this address is and 4:37 - then it may have come back with the 4:39 - number so it may require more than one 4:41 - hop to a different dns server but 4:43 - eventually no matter what name you type 4:45 - in it will come back there is an 4:48 - international body out there that 4:50 - decides who can get what name you cannot 4:52 - just go ahead and say hey can I be 4:54 - microsoft.com so what happens is you can 4:57 - register different names and you can go 4:59 - out and register names for yourself so 5:01 - you can have your own custom or vanity 5:02 - name or if you have a business you want 5:04 - to start up you can get your own name 5:06 - and then you what you do is you register 5:08 - that with an agency that associates your 5:11 - name with a real-world physical address

11 5:14 - and this is a controversial topic there 5:17 - are a lot of each country this is a 5:20 - controversial topic there are countries 5:22 - that control their own rules for how you 5:24 - can get a name 5:25 - so for example if you want to. CA 5:27 - within canada and then there's other new 5:30 - top-level domains such as. see a dot ed 5:33 - u dot org and each of these have their 5:36 - own rules for how you can obtain your 5:37 - own name at the end of the day though 5:39 - your computer just types in eight at the 5:42 - end of the day though you don't have to 5:44 - really worry about this you type in a 5:46 - name and they at the end of the day 5:50 - though you don't have to worry about 5:51 - this you just simply type in a name and 5:53 - your dns server will resolve that to an 5:55 - IP address now I mentioned that there's 5:58 - only four billion IP addresses out there 6:00 - how do you get an IP address 6:02 - well there's two categories of IP 6:04 - addresses this fixed IP addresses and 6:07 - big companies like Google and Microsoft 6:09 - have their own fixed IP addresses as 6:11 - well as organizations like the 6:13 - university of waterloo in fact every 6:16 - number that starts with is an 6:19 - actual University of Waterloo 6:20 - address what university of waterloo has 6:23 - that entire range but you're just a 6:25 - regular citizen and you want to connect 6:27 - to network whether you're at Waterloo or 6:30 - starbucks or at your home network and 6:32 - each one of your device's needs an IP 6:34 - address 6:36 - well the way these on the fly or 6:39 - temporary IP addresses are doled out is 6:41 - known as dhcp which stands for dynamic 6:45 - host configuration protocol so the idea 6:47 - is your device when it turns on and it 6:49 - tries to connect to a network it's sort 6:51 - of sense of message out hey I don't have 6:53 - an IP address can i have IP address

12 6:55 - please 6:56 - and then what happens is there's a dhcp 6:58 - server out there that has a bank of IP 7:01 - addresses that it can give out and what 7:03 - it will do is will give you an IP 7:05 - address that you can use and it also 7:07 - will expire after a certain amount of 7:09 - time so if you go to starbucks and 7:11 - starbucks gives you an IP address that's 7:13 - great but an hour later when you're gone 7:15 - someone else can get that same IP 7:17 - address and so the dhcp server just 7:19 - keeps track of addresses it has 7:20 - available and told them out as needed 7:23 - this is especially important for your 7:25 - mobile devices like your phone and 7:26 - laptop swear you may connect to multiple 7:28 - different networks now the last tricky 7:31 - piece I want to explain which will 7:33 - really help your understanding of how 7:34 - communication on the internet works is 7:36 - known as network address translation and 7:39 - when you connect to your home network or 7:41 - even starbucks or places on the campus 7:43 - this system is used so that we don't run 7:46 - out of IP addresses so how not actually 7:49 - works is a little complicated and I 7:51 - don't want to get bogged down in details 7:52 - so what I'm going to do is give you an 7:54 - analogy using physical addresses that 7:56 - will just give you an understanding of 7:57 - how basically it works so let's say we 7:59 - have an apartment building and that 8:01 - apartment building has a physical 8:02 - address known as 555 real street that's 8:05 - real physical address in our world but 8:07 - there's a whole bunch of people who live 8:09 - inside the apartment building and they 8:11 - don't even know they're at 55 real 8:13 - street they all think they live at 8:14 - imaginary lane one person might think 8:16 - they live at 100 imaginary lane and 8:18 - someone else might live at a hundred and

13 8:19 - one imagined 8:20 - Elaine so you might think you live at a 8:22 - hundred and one imaginary lane and then 8:24 - you want to send a postcard to your 8:25 - friend who lives at destination avenue 8:28 - so you fill out your postcard dear Bob 8:30 - at 789 destination avenue and you return 8:33 - address you put as a hundred and one 8:34 - imaginary lane and then what you do is 8:37 - you hand your postcard to the nice 8:40 - doorman who lives at real street 55 real 8:43 - street so you say hey doorman can you 8:45 - please deliver this postcard for me he 8:47 - says no problem and then what he does is 8:50 - he changes your return address to be 55 8:53 - real street 8:54 - unbeknownst to you and then he sends out 8:56 - the postcards the destination avenue and 8:58 - then your friend of destination having 9:00 - you get your postcard sees your address 9:02 - is 555 real street and then sends it 9:04 - back to you and then when it arrives the 9:07 - doorman looks at your postcard ago Zaha 9:09 - this is my friend who lives at a hundred 9:11 - one imaginary lane and again changes the 9:13 - address from real street back 201 9:17 - imaginary lane and then passes the 9:19 - postcard onto you you were completely 9:21 - oblivious to this whole thing the 9:22 - doorman was doing all of this managing 9:24 - for you 9:25 - so what happens is we can have hundreds 9:27 - or even thousands of computers all 9:29 - sharing the same physical address and 9:31 - this is another way of getting around 9:33 - this problem of running out of IP 9:35 - addresses so when you go on your 9:36 - computer and you ask your computer hey 9:39 - whats my IP address it might come up 9:41 - with a number such as imaginary lane and 9:44 - in fact if your IP address begins with 9: you live in imaginary lame 9:50 - alright we just discussed a few 9:52 - technical issues that help us understand

14 9:54 - how the internet works and how the 9:56 - internet protocol works but let's 9:58 - actually talk about Internet routing 9:59 - because that's one of the core parts of 10:01 - the IP protocol whenever your computer 10:04 - sends out a message it has a destination 10:06 - IP address and your computer sends that 10:08 - to a local router and that router may 10:11 - send it to another router 10:12 - another router and then another router 10:14 - and eventually you'll reach the computer 10:15 - that it wants to reach all of these 10:17 - individual routers are all connected 10:19 - together and are constantly sending 10:21 - millions of messages back and forth back 10:23 - and forth and that's how your message 10:25 - gets from one side of the world to 10:27 - another side of the world 10:28 - how does this work let's discuss how it 10:30 - works in the real world say you live in 10:32 - kitchener waterloo and you want to send 10:34 - your postcard to someone in England 10:36 - well you fill out your postcard and you 10:38 - get someone's address in England and 10:40 - then you take it to your local mailbox 10:42 - and then someone picks up that postcard 10:44 - from the mailbox it takes it to a 10:45 - central depot and they look at the 10:47 - address and they say oh this one's going 10:49 - to England so i might send that to the 10:51 - central Ontario dispatch I don't know 10:52 - how it actually works in the real world 10:54 - I'm making this up but we can imagine 10:55 - that it goes to a central Ontario 10:57 - dispatch and they look at someone looks 10:58 - at the address there and goes all this 11:00 - is going to England so they take it to a 11:01 - candidate dispatch center and then at 11:03 - the candidate dispatch center they look 11:05 - at this address and go all this is going 11:07 - to England well let's put it on this 11:08 - boat that travels to England and it goes 11:10 - over the see me on some sort of big boat

15 11:15 - and he gets over to England and then 11:16 - someone opens it up and goes I ok well 11:19 - you want to go to London England so 11:21 - let's put it and let's give it off to 11:23 - someone who delivers in that region and 11:26 - then eventually you'll get narrow and 11:28 - narrow and smaller and eventually it 11:29 - will show up at someone's house so this 11:32 - idea of each person who looks at the 11:34 - postcard along the way nose in general 11:38 - which direction the postcard has to go 11:40 - and it's complicated but that's how all 11:43 - the network routers on the internet work 11:45 - whenever you send out a message each one 11:47 - of them send it to another router that 11:49 - will get you closer and closer to your 11:51 - destination now it's hard to visualize 11:53 - how all the routers in the world are 11:55 - connected i stole this photo and this is 11:57 - from 1999 so this is even a long time 12:00 - ago but this is a visualization of many 12:02 - of the routers that exist in the real 12:04 - world and so you can see how you might 12:06 - start in one corner of this giant 12:09 - network and make your way through a 12:12 - whole bunch of different paths to your 12:13 - destination at the other side of the 12:15 - world in general every message you sent 12:17 - on the internet takes less than 50 hops 12:20 - and a hot being goes from one router to 12:22 - another 12:22 - router that's still a lot but you can 12:24 - reach almost any computer from any other 12:26 - computer in the world within about 50 12:28 - hot and that's how all the messages on 12:30 - the internet get transmitted