How does the Internet work?

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Video in TIB AV-Portal: How does the Internet work?

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How does the Internet work?
An explanation of Inter-Net and everyday protocols
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You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor.
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This Foundations talk explains the systems and protocols that make up the Internet, starting from a laptop with a Wi-Fi connection. No particular technical knowledge required.
Keywords Resilience

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[Music] welcome everybody to this talk how does the internet work and our speakers Peter stood and I'm very happy that is here to explain to all of us how the infrastructure of the Internet really works I'm pretty sure we will all learn a lot today please give a big and warm round of applause for Peter Dugan
thank you very much thank you for being here this is amazing translation of into French Wow so I want to talk about how the internet works and I try to try to yeah try to shine some light on all the technologies that are involved when we use the internet every day so why this talk some motivation first then a little bit of brief background just how the internet got started then we get into the details so what actually happens between the web browser and the website that's that's the starting point so in the description I I listed things from bottom up so from the very low-level packaged stuff and through the various layers of the network stack up into the applications and that's the building blocks part but I inserted this this overview first what what is actually going on between the browser and the website because that's what most people already know and use a lot some some parts well some details about the different protocols and in the end some recommendations for further talks if you find these these topics interesting so the the reason I want to give this talk is to to talk about how does the internet work right the the mechanism that we use all the time but aren't mentioned very much so they they are sort of obscured or well I don't know if hidden is the right word but we wouldn't we don't experience the network itself very much right we experience the various services that we use and they the services they try their hardest to to keep us interested to to fancy tickle our our imagination and I think I think it's dangerous to not talk a little bit about the network every now and then and to think about the network and to actually fight for a public network that is available to all and and equal also neutral if we if we focus on the service providers alone then they're going to be deciding what we can do with the network but the point of or the great thing about how the Internet is neutral today is that we are all connected or we could all connect to each other we don't really have to use these service providers we tend to this is somehow a human nature to sort of go towards centralization and monopolization but the Internet is a tool that would allow us to try more more variants or or other other kinds of structures and we need to we need to be aware of that and the importance of net neutrality if we don't talk a bit about
the network we might lose it so how did
it all get started in 1970 then our
power they started the ARPANET so our pub back then is now DARPA that's the Defense Advanced Research Projects Agency they develop technology for the US military and they did back then as well so the ARPANET was as as the quote says from this very very old document that objective is to get all their suppliers connected into a network together and and being able to exchange information so that they can I guess make progress more more quickly more efficiently right now it's something else I think that's good
so let's let's look at what happens between the browser and the website so
we have a person using a laptop and they have a browser and they they type in a web address events cccd for example to read the blog post the latest blog post about congress so then the browser really does two different things first of all or to get to show this page so first of all it has to ask for the the way to reach this website that we want to reach computers they don't they don't deal very well with names or text at least enough network the network part of computers or our systems so there's this translation somehow like a phone book I'll get back to that in a bit called DNS which is used primarily it has a few other uses as well but it's used primarily to to get from this name that we entered events CCC de that we can also somehow easily remember to the the network address the IP address of this website so that's part one and it says System DNS because the browser doesn't do all of this phonebook lookup itself it can rely on the operating system to take care of this fortunately so that's the parentheses that's what operating system is doing it's using a few protocols UDP IP and that becomes a network packet we'll get back to those
in just a little bit so once the browser has the the network address the IP address of this website it it creates a connection so it contacts the the web server and it uses this this set of protocols so it first uses IP to to reach the IP address of the server and then particular it uses TCP for this connection type and get back to those in a little bit as well what what their properties are and on top of that the browser then uses the HTTP protocol an example of that in the Marion howl or two to get to request the the webpage that we wanted to see and that's all happening on the laptop in the browser and part in the operating system that we're using whatever that might be then there's of course this long chain or or sometimes not so long but usually several several machines along the way routers we might have a wireless router at home or in a coffee shop or here at at Congress and beyond that there is certainly there are certainly some more routers along the way from or between our laptop my laptop and the destination that I want to contact so all of these routers they they receive some some packet they look at the addresses where it's going in particular and then sends it along its way so they're they're just forwarding packets all all day long finally at the destination on the on the web server there are also two two parts so first of all the that the request that was sent by the by the browser is received it goes through these these different different layers these different protocols and the website server software it's it looks at the request and it sees okay somebody wanted the first blog post then I'll send that right back the same way that I received the request and that's part two so returning their response to this request and it goes all the way through the the routers the same like the same path but in the reverse direction to the laptop so let's let's look at all these these
different building blocks all right so let's start with the small smallest one in the network packet I talked about packets going back and forth so the packet or a packet is sort of the at home on the network it's the smallest useful unit that is sent or processed by the network I I think a good way to explain packets is with regular postcards that we can send with mail because their size their maximum allowed size is pretty much standardized it's it's you can't you can send a postcard which is one meter right and it's the same in the network packets you can't send arbitrarily large network packets one pretty common maximum size is 1500 bytes or roughly characters so just to give an idea of how fairly small the packets are actually and even that might
I don't know do 1500 characters fit on a postcard no I guess not I think that's too much so maybe the packets are a little bit larger than postcards but but still the the analogy is is pretty good because you send them out and and there's very little there's a little bit of structure like there's a stamp perhaps and a recipient address but that's pretty much it what you what you write on the postcard on the on the other side is really up to you and it's the same with the packets they can contain anything but if you write in a language that the receiver doesn't know then they're gonna receive the packet and then actually just drop it because they don't know what you're trying to tell them so packets they are sent and received through network interfaces this is a an Ethernet cable LAN port or a Wi-Fi antenna or maybe a 3G 3G modem if you're on the go out and about and your cell phone does this of course as well right the cell phone has Wi-Fi if you're in a coffee shop maybe or it has 3G if you're in the subway or on the tram and one interesting thing or where the comparison to the postcards doesn't really really fit anymore is that network interfaces they can they can easily pass millions and packets in
a single second so it can be can be quite a lot of information going going through especially if you have a good internet connection like here at Congress so then the next next step or sort of if you start looking at okay what can we put on the on the information side of the postcard right where where we can put any message we want for for this talk I'm only going to focus on an IP version 4 I know it's it's old and an legacy and we really shouldn't be using it though but it is it's it's it's dominant so far it won't be forever but so far it's it's quite common and I think it's it's something
that most of us have at least seen when setting up the Wi-Fi or or the new internet connection right this this IP address that I put up on the slide is maybe the most common IP address there is right for that for the new wireless router these these IP addresses they are consists of the four numbers and they are the four numbers they range from 0 to 255 and then there's 4 of them and with dots in between it's just how we write them this is an efficient way for for machines to identify themselves but the reason IP version 4 isn't so great anymore is that it's it's quite quite a small number of addresses so it turns out that the Internet is pretty popular and worldwide the addresses are have run out or are running out there's there's there's there aren't enough addresses for all the devices that are actually participating or somehow connected to the Internet ipv6 will solve this let's see maybe maybe we'll live to experience that so what is what is a network then there are different kinds of networks I've written physical networks and logical or
abstract networks physical network is cabling right if you have some kind of connection from your internet service provider it goes to your wireless router and you have a or if you have a LAN set up like in the hack Center with the switch and lots of cabling cables to each one cable to each computer that's a physical network and that's a tangible thing right than something we can we can touch and we can modify it with our hands and and so on but then there are also and that's that's one certainly one network type and another equally valid network type is the logical network or as I'm also call it abstract network which is defined only by the addresses used by some set of computers that are communicating together so here's an example of an IP network that might be used with the wireless router that that's has the IP address up on top right and the there's sort of a pattern right the first three digits are the same and that's the address that the network address and the very last part
is this is 0 with the slash 24 meaning the 24 first bits of the 32 so now it's technical maths and binary and sorry but essentially the the 24 means the first three numbers are always the same and within this logical network so within this group of computers or systems that can communicate with each other only the very last digit will will change and as long as this is this is the case we don't need a router yet we can all these computers or all these systems they can communicate directly with each other on the local network or on a Wi-Fi or or whatever and the slash 24 and with the 255 255 255 0 that's just two different ways to express things actually the same thing so where do these these IP address IP addresses come from and and how who has them and and so on so if we if we get a wireless router then then we have some IP addresses but me and my friend we both have the same perhaps IP addresses because we have a wireless router from the same supplier right and this is a little bit of a special case those aren't internet IP addresses they're used only only very locally so only in in one home network only in one
company network perhaps the the public IP addresses are the ones that are on the outside of this this wireless router that I got and the wireless router typically only has one some some eternal providers give you a few but it's very easy to have a lot more devices in your home or in your office than public IP addresses that you get from your internet internet provider so the IP address is there assigned to the internet providers and or the other way around I internet providers they apply for some some range of some number of IP addresses and here in Europe there's an organization called ripe in charge of allocating a block of IP addresses to the internet companies that are actively connecting to other Internet companies and and maybe are also your internet providers and and mine so and and ripe they have they of course have colleagues in in in different parts of the world so I think there's four or five maybe even six of the ripe organizations the regional network
centers they assign IP address blocks to the internet companies and by internet company I don't only mean internet providers that that we use at home and and at work but also really any larger company that has a service available on the internet so all the streaming sites that you can imagine all the I'm most well several large just websites that are used every day will also have their own IP address range and will be active in finding different ways to connect to the internet providers so that the end users can have as good an experience as possible when they're visiting there or using their services so I talked about
the internet companies they are trying to find good ways to to to connect to each other or to make it possible for users on one with one Internet company to reach either users at another internet company or some service provided by by some internet company and that's that's the routing that's going on both in the wireless wireless router at home but just as well and and even more so in in all these routers on the internet that are handing packets back and forth so starting with the wireless home router it typically has one local network at least it might have more so I
had a home router that had both the the regular Wi-Fi network and I was also able to configure a guest guest network or a guest password so that's actually - its Wi-Fi so it's not released but those are two separate physical networks because if you're connected to one you can't communicate directly with the other network without a router now there's there's some chance that the wireless router will do this will enable this communication but it's not for sure and it's not it's not certain and in fact it's more likely that it won't work because this guest access you're supposed to be able to give that to somebody who's just visiting and maybe you don't want them to access your your printer or your your storage cabinet or or whatever right so it's quite likely that this guest guest network doesn't get access to the main network so two different networks even though it's it's the same the same radio waves or the same air that's carrying the radio waves but the the key key property by the or with the wireless or a home router is that it almost always only has a single internet connection so it has a single connection to some internet provider or in in the direction of the internet typically that's that's the the taco but in some cases there's even especially in the u.s. there's the situation where the telco or the internet provider is also an content service provider and that's
that's a pretty bad situation in particular if you have no options no choice so we have the home router with a single connection towards the Internet to the internet provider let's compare that with the Internet routers that are further out on the internet and operated by the many different internet internet companies they they will similarly have one or more local networks that that belong to them the same way that the wireless network belongs to the home router a wireless wireless company or a sorry an Internet company or an Internet organization let's say like the CCC as well has some some equipment some servers with the the events CC CBE server for example is is part of the CCC slice of the internet and the router that's that's responsible for for all of these networks has like is responsible
for also this this IP segment that where the web servers now the the big difference here is that those Internet routers or the the routers that are further out on the internet than our home routers they typically connect to at least two but usually many more other Internet routers exactly how is is different in every location there are some some norms and some some common topologies but this is so the connections that exist are determined by by peering agreements between the the internet companies and their internet organizations there they can of course have agreements with whoever so it's it's not so easy to tell beforehand what a particular organization how a particular organization will do peering this is an interesting topic there are some more toxin on this as well and that I'm referring to later one at least one model is to have a site some some data center somewhere where an internet exchange is running so this is an organization whose sole purpose is to enable many different internet internet companies or Internet organizations to somehow make their way there put some cables to this this data center and all connect together and be able to exchange traffic between each other efficiently and maybe even at no cost that's that's an interesting interesting topic because there are so many different business models for for this peering for the peering agreements so the internet exchange is one one model there's there's a handful of them in in Germany and yeah that's that's about the scale of it private peering is of course possible to where organisations just have a direct connection between between each other and okay so these connections they are then established somehow and how to how do the routers know where to send what and answer that's a good question this is managed by routing protocols BGP is is one one such application or some bird is one application and BGP is the protocol so there's there are some rules you can configure what to prefer what what route refer but you can also just say I don't really care so much and just use whatever is available and of course this depends on how much you have to pay for traffic that you send which way if you have a really good pairing agreement with another internet organization and your you're able to send a lot of traffic there way then without having to pay very much extra or maybe anything at all then of course you're going to try to send as much traffic as possible that that way all right so now we're getting we've
looked at IP addresses and IP addresses we know some systems on the internet or connected to the Internet all of all systems connected to the Internet they have some IP address and if we know the IP address we can try to try to reach that system you know yeah you know that's a bit unfortunate so that the first the first bullet point is UDP it's now we're talking about okay so on the on the postcard when we're writing stuff there we we put the IP address because we know what system we want to reach but we want to send it
some kind of message as well there are a few few different ways to to structure messages and these are the most common ones or the ones that make up almost all of them the traffic on the Internet so the first one is UDP it's it's quite like postcards so it's just a single message there's no there's no context there's no connection between two different messages and there's also no guarantees about how this message will or this packet will will perform on the network so if you send out a UDP packet it might arrive or it might not and you'll never know and that can seem a bit useless but actually it's it's quite it's quite good in in many cases for example if you're doing real-time real-time audio or video streaming UDP is a good choice because it's real-time information so if something is missing maybe there will be a glitch in the in the audio or there will be some glitch in the in the video but yeah that it's not so important to wait and delay the the image to fix that glitch it's better to get the next image and just replace the image so just keep keep on keep on going and for that UDP is there is a really good fit it's just send it send it along there and if it arrives it arrives most of the time it does arrive most of the time it
works fine so sometimes a good choice the next the next point there is TCP so maybe you've heard the term tcp/ip and tcp/ip is exactly the so specifically it's the combination of this is TCP that I'll get into in a second with the IP addressing both TCP and UDP they they have the concept of a port so that's a second second address you could compare that with let's say the IP address is
the street name and the port is the the number the house number on that particular street so it's a bit more precise you know it's that system but that system might have many might offer many services and you want one specific one so for each of the common services that we use email and and web and jabber and whatever there are typical typical port numbers that are allocated and always the same so that I don't have to guess or or look up what it's what it is so with the TCP what what are the properties of that that's that's more like a stream of letters that you have
to go to the post office and and acknowledge that you've received so the the recipient of a TCP packet or a network packet with IP and TCP inside of it will always confirm reception to the sender so this allows this concept of a connection that I mentioned where both sides talking to each other or are synchronized and know where the the other party is in this communication or in this connection what data has been received and what has not yet been received so did the packets TCP packets can of course also get lost right there's there's no guarantee with with any network that it will always function correctly you can just pull the cable and it will not be possible to send any packets so TCP will will recognize that oh so I sent some packets out but they haven't been confirmed they haven't been acknowledged okay I'll try again I'll send send again a few times and it's it's usually adjustable how long
TCP will be retrying to communicate and finally it will give up and say yeah sorry that seems that this connection is broken I'm it's not possible to to communicate anymore over this over this path but if you're quick and you plug the cable back in and then maybe everything will will heal or the connection will just continue functioning just as if there was never an interruption because the the network software is this keeping track of what has been sent what has been received and can recover from from this loss of communication and the third one on the bottom is SCTP this is not not quite so widespread but it's it's still a very powerful mix it's it's a lot younger than the other two so UDP and TCP there from those images I'd like to say 70s and 80s yeah so quite quite old whereas SCTP is I think the standard was was final in or the first version of the
standard came in 2000 so it's quite a lot younger this this protocol but it's a powerful combination of properties from the both the from the from the older ones so you can have whereas TCP you just have a constant stream of text essentially or image or whatever content you are transferring with UDP you had this message that's on the postcard like it's one postcard that you're sending that's the fixed fixed message TCP doesn't have that concept it's just just information all the time until the connection closes SCTP you can have a connection concept where both sides are aware of the communication status or the position and in the communication but you will be able to use that you will still be able to send messages like on the postcards or like the postcard so you have a fixed fixed size piece of information that you want to transfer and you can you can send that as a as a unit whereas if you're only using TCP like we do on the web all the time you have to build a lot of stuff around or on top of TCP in order to achieve the same thing so if I want to transfer an image or when my browser wants to download an image there's quite a lot of extra work that has to go into making that possible with the regular TCP protocol that that is being used for now so the advantage SCTP certainly it also has the the retry of the reliable delivery if you if you want to and you can also use multihoming so that's not so common yet as I said typically the wireless home routers they only have single internet connection but that
might change we might in the future see several different kinds of internet connections that that we're using and SCTP would be able to take advantage and that quite easily whereas the other ones cannot and so as it typical send the same information over several different connections and whatever comes first arrives first at the destination is accepted this is of course a bit wasteful but in some cases maybe it's not a problem so that's that's an exciting I think exciting new feature let's see what the future brings it seems that it seems that TCP is is going away slowly but surely let's see what happens but then the some some some companies they're providing systems where they want they want to control much more of how the the software is using the network how the software is communicating on the network and the way that these systems are built cell phones typically or smartphones it's not it's not so easy to do that with either TCP or setp
but it's quite easy to do it if they're using UDP so I think that's a big motivator for them to to try to move away from TCP and and use UDP even more let's see sorry
so then we'll get into some applications now we've we've written on the post card with britain addresses IP addresses the system that we want to communicate with and we've chosen either UDP or TCP depending on what what is most suitable actually it depends typically on the application so some applications require one or the and a few applications can do either or the first thing I'd like to mention here is DNS I call it the phonebook the internet phonebook so but there's one big difference a phonebook is something we get from from one publisher right the phone company typically and they or or the POC here at Congress and they they've just collected or they know all the phone numbers and they send us the list right with the names DNS is different in that everybody who has who has a name in the DNS and the domain name system so anybody can register a domain name and anybody who does that can can publish some information there you can decide what you publish actually you can decide if you publish it so let's say you have a thousand IP addresses you can decide if you want to publish names for all of those thousand or if you just maybe publish a few of them that are going to be interesting for other people to use and 90% of them are of just internal internal systems so everybody gets to choose what they what they publish and everybody can publish also can can run the infrastructure storing this information on their own so it's not that you have to send this in somewhere necessarily and they
publish it for you you can actually do that on your own so it's decentralized very good still it's a super super old protocol also from from those days of from those early days of the internet and nobody was thinking about security and nobody well nobody had done a lot of attacks on whether it on these protocols whether it be reliability attacks or or just forgery attacks and that wasn't a concern because this was remember designed for companies working for the government right so everybody was interested in collaborating and there were no bad actors the internet now is again quite different so some of these is old while most of these old protocols actually aren't aren't so great anymore basic functionality of DNS or the phonebook is to publish IP addresses but you can publish other things as well if you're interested in in DNS there's a good good talk about that later on I mentioned in a bit so the next application I want to talk about is is SMTP or the next application protocol Simple Mail Transfer Protocol this is what is used to deliver every single email in the world all the time all day long now one thing that's a bit
bit interesting or quite interesting but also problematic I'd say about email and and not SMTP per se perhaps but the scope of SMTP is that SMTP is used only to send email so SMTP doesn't have anything to do with receiving email this means that there's a so there's a separate separate mechanism for receiving email and the way these two these two different protocols or mechanisms work end up putting the cost of email with the person receiving mail so I have to pay in order to either with information or with money to get an email address where I have some some gigabytes of storage whereas people sending email they don't have to pay anything they just need the internet access and then they can send all the emails I want all day long to every single possible address email address in the world and that's why we have a spam problem on the Internet so this is um yeah it's a bug I let's see if this can get fixed email is so tightly integrated into our everyday lives that I'm not
sure but let's see that would be great so on the the last one the last application protocol I want to mention is the HTTP hypertext transfer transfer protocol that's used for web right you recognize it from the from the web browser URLs web pages used to be just hypertext so text with some links and them that's all all they could do in the very beginning and I'd like to show an
example of SMTP actually this I I have to do something about this because it's not so it's not so easy to read let's
yeah I should have done that already
sorry about that so this is an example of an email delivery this is this is all it takes to send an email on the internet and the the left and the right on the on the edge there is so the arrow pointing that way right left is risk
received from the email server so from the SMTP server and the arrow pointing this way is what we send to the email server when we want to send an email so
if we connect to an email server for example mine it will say send us some text we're using by the way TCP and we're using port 25 for for SMTP so we get a stream of text going back and forth the the server tells us 220 and its name that's some kind of welcome code we say hello I'm I'm my name is laptop because I'm doing this for my laptop the the mail server says ok good to meet you and then we say I want to send an email where the sender address is test at still give dot se and if you're paying attention here the sender of the email gets to gets to say what the sender address is so this is why it's super easy for anyone to forge email from any sender address this it's just it's part part of the message or the part of the the yeah part of the message server accepts the sender even though the sender might not even exist I tell that recipient this is for me me for me it's and server says ok then I say here's the data for this for this email and the server says go on start start sending me the contents and then I send send an email where the sender is tralala lala land just some fake fake sender address whatever subject and some text and in the end I've finished with the dot to say okay and a message and mail the services okay and then I say to the server I want to quit now I don't want to talk to you anymore the surface as closing goodbye this is this is email on the network last example a webpage access over HTTP so this is even even simpler I've simplified this even a little bit more if you try this try this yourself please do so HTTP is also TCP and port 80 I tried talking to the events CC CDE web server and I told it same thing here arrows pointing this way is is what what we send when we contact the server so connection opens I send get slash and HTTP one dollar because I want to get the main page and i'm saying i'm i'm speaking HTTP version 11.0 okay i want to access this start page on on the hostname events cccd then I send it an empty empty line that's to say okay this is my my request and then there comes the response comes back for the arrows going in the other direction where the webserver says actually so what you're asking for it's not available here where you're asking for it you have to go somewhere else it's a redirect that's the the 301 is the code for HTTP code for redirect and this this contents that you're asking for this page it's been moved permanently the new location is HTTP events CC CBE so I was using an an IP and TCP connection with no encryption and that's why I can just type in the the get and the host line but the web
server tells me a sorry I don't want to talk to you without encryption so you have to go to this HTTP address instead thank you event CCC de I like encryption that's good and thank you also to all the angels that make Congress possible
because without them and without you who are here who who are angels that there wouldn't be any Congress and also I want to say a huge thank you to you in the audience for being curious and and wanting to learn something new [Applause]
[Music] thank you very much Peter now we have some time left for Q&A so if you have questions please do line up at the
microphones that you find here if you want to ask anything do we have a question from the Internet no the Internet is out of questions we'll see anybody standing at any microphone please make yourself known if I overlooked you any questions oh I'm sorry but no I I don't so there
was that I mean I wish that that would be great it's not so easy to fix because because it's it is a property of SMTP right and of the email system that we're using so there was a proposal a long long time ago by somebody much smarter than me called internet mail 2000 where we're actually the whole thing is switched around so that the sender has to store the message and the receiver can go and pick it up so there the cost is is is placed on the sender and I think that would go a long way to solving the spam problem but it's also it's not compatible with the email software that we have today so I don't it like there's it's not clear to me how we would be able to migrate in in a in a good way unfortunately thank you do we have any other questions that does not seem to be
the case so please if another one round of applause to clean us to the thank you very much capital thank you [Music]