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If somebody sends you an ARP packet specifying designating you in the target position, then you obviously have to answer their question and provide the answer. At the same time, you have to store the mapping provided by the questioner, the guy who sent the ARP request, because it provided in the ARP packet, the ARP packet, the ARP packet, the ARP packet,

capture this and overwrite our cache because that's the most up-to-date mapping. So just in case your mapping is stale, out of date, that overwriting will automatically update your cache entry as far as that questioner is concerned. And it's the same for the other guys even if you're not the target.

protocol is not you so you're not responsible for providing the answer but even in that case you can have a mapping for that question you do the same overwriting operation so that your cash entry is automatically updated so that's a simple rule very very simple and one of the applications of such rule

was the gratuitous ARP and I'm going to show you the opcache, sorry, the wireshark packet trace. I got this just before the class, okay? A minute before the class. The filter that you should use ARP dot is gratuitous. ARP dot is gratuitous. You may not see it because it's too small here.

ARP dot is GraduTus. Okay, so this packet is GraduTus ARP. It's shown. Okay, so we got two of them. So let's inspect these two packets. The second one is not the same guy. So let's see this.

can see that the target and the sender IP addresses are identical. This is the sign that this is a great tutor CRP. This guy is asking himself, like me calling Kimi-ho-ba, and make sure that there's no Kimi-ho-ba in this one. Just like that. So that's why you put your own IP address in the target IP position in the greater CRP. If nobody answers, very good.

that's the expected outcome but if somebody answers then that's a problem you have to resolve that problem but it's out of the scope of this protocol itself some some some action must be taken by the administrator or something yeah this is an old gratitude therapy in the sense that he provides this mapping immediately but in the most recent version this is not done I mean this is a simple it's a single step process credit to therapy this old one the single stop step process you just send this is send this

request and if someone receives this and it finds that it has an ARP cache entry that map that has this sender IP address 84 then it will overwrite that entry with this mapping provided in the greater concern. Okay, immediately. But this is kind of dangerous because it can poison the other guys in case my IP address is being used by someone else already.

Maybe I'm the perpetrator. Maybe I'm the culprit. So in that case, I will override their cache-in list with my incorrect mapping, 'cause I'm not supposed to use this item because if someone is already using it, right? In this case, I'll just poison the cache-in list. So to prevent this, we have a newer version called ACV, which works in two phase manner. In the first place, it checks DAD.

first it checks the AD without poisoning the outcatch by doing, by providing the source I did this with 0000. So some invalid I could, we'll talk about I could provide 0000 in this position, this mapping is in there.

so they will not override the entry even if they have this one because it's zero zero zero zero never matches it so they will ignore it but not override it so the guy who sends this ACD will check if there's anyone who is already using 84 and in the first place that will be revealed okay so if someone is using

the question I would get on the 5. In that case, you will not commit. Commit is not good. But if all things are fine and everything's fine, and there's no one that answers this question, 84, in the target I could press, then it's fine. Then you can go ahead with the second step, second phase, and commit the method. So ACD is done in two phases.

So in ACV, let me see if there is actually ACV.

announcement. So you can check if there was an ACD packet. Oh yes, there was. So this is an announcement, the first phase of the ACD. Okay, so we're doing the same thing in a different manner. So in this case you can see, whoops, is this really enough? No, I don't think this is ACD.

still great uterus in the sense that it doesn't provide 0, 0, 0, 0 in the send argument. I think this is Y-shark. Bug. This is not correct. Okay, anyway, so this is a good example. Let's go back to this guy.

- Mm.

I think this is incorrect. So you have to move this. This is not ACD, it's the graded to therapy. ACD appears in the next slide. So this is ACD, where the source protocol is set to 0000. So in the first phase, you send the ARP request with 0000 as a source. Like graded to therapy, if a request received is abnormal. So conflict is...

discovered. If no reply in the second phase, what you do is to set the source protocol to your desired market address and we send you an AOP request. That's called, is this an announcement? Oh, sorry. I was wrong. So announcement was the second phase. Ah, right. So the first phase was called probe. So Bioshock was correct. Okay. So this is the second step. This is the commitment.

it provides the correct sender

have some probes. Yeah, as I said the sender I give this set to zero zero zero zero to avoid poisoning other cache entries that might have 84. So you first do this. So you send this in the first phase and there's no response that's absolutely normal and you go ahead with the second which is announcing. If you have an old mapping just override it with this so that you can automatically update your question.

also okay so this is a review of what we discussed last time any questions about any questions no all right so we'll skip the rest of the chapter two more special therapy cases proxy and our team and directed it up so you read the textbook the reason is we are lagging behind a little bit so that's why i'm going to skip the rest of the chapter and go to chapter four

is about IP. Now, that's the value about data link. Data link has a lot of functions in itself, but IP doesn't care about the details of data as long as it provides three functions, three information. First of all is encapsulation, and the second one is ARP. in the previous chapter. And the third one is MID.

the end of the semester. So that's all. That's all IP need to know about . Now, let's move on to the third layer of the protocol step which is IP in our case. IP is the only one that's there as far as user data is concerned. So user data always has to use IP because IP data is a standard container for any data that's moving across internet. So there's no other.

we don't have to memorize other protocols. IPs do not need. So in chapter 4, we are going to discuss the address structure of an IP that's used by IP. So you will be familiar with this IP address format, which is called "Dotted Decimal Location". So four decimal numbers separated by dots, like 163 dots, 115.

152.1.1, for example. But this is for human readability. I produce this in computer. It's just a 32-bit binary number. But you don't remember binary number very well, right? So that's why we use this notation for human convenience. So if you provide this on a command line or anything, I mean, in URL, you could do that also. but it will be translated to 32-bit binary string

by the computer before it is used as an IP address. The real IP address is just 30 to be binary number, not this, this is a character string. Okay, character one, character six, character three, character dot, blah, blah, blah. So it's a character string. So it has to be converted to 30 to be binary number before it is used by the network. So here, right, so this guy, 46, 161, 46 is

this in the computer. And there are three IP version 4 address types. The first one is unicast, the second one is multicast, and the third one is border-cast. Sometimes we refer to these as cast types. Because there are different casts. Unicast, uni means one, so it's one-to-one type of address. So it only identifies a single interface. Single interface.

Usually we talk about computers when we map IP addresses. So each computer has an IP address. Well, it makes sense, but technically it's not correct. Because IP address is given to an interface, not a computer. Okay, computer, like your smartphone, can have multiple IP addresses. At least one for each interface. I mean, an interface can have one or more IP addresses. So a more technically correct description is that each interface has an IP address.

IP address is given to an interface not the computer. So unicast address is given to an interface so that IP datagrams can be sent to that interface. Multicast means that this IP address identifies a set of interfaces, a group of interfaces. So you send one IP datagram to this multicast address it will be delivered to multiple interfaces at the end.

It's a magic, right? Because you sent only one. Now how can it be delivered to multiple interfaces, multiple destinations? Well, the magic happens inside the internet. The router, I mean routers inside the network makes copies, okay? So if you send out one packet, routers can copy and send out over multiple interfaces. and it can happen many many times

and finally this tree will expand and expand and expand and finally they will reach the final destination so that's why that's how the multi-cast is achieved but you sent out send out just one pack it'll be replicated to many many copies as many copies as there are members in the multi-cast group and we'll We'll discuss that in some of the later chapters. Finally, there's broadcast.

A broadcast means a packet is delivered to everybody. So what everybody are we talking about? Is it everybody on the internet? Of course not. So when you talk about broadcast, there's a scope of the board. We'll talk about that in this chat. Okay, first of all, IP address is asserted to be a big number, but it's not a monolith. I mean, this whole space is not an analytic space. It has a structure.

and the structure reflects the structure of the internet itself okay first of all we have so-called five classes what is the notion of class? is the size of address and location how did you get your address at home? Your internet community or basically home router has an ID address.

how did you get it do you know how you got that IP address it started from somewhere right and finally reached your device and was assigned to your device do you know the story how you how you end up I ended up getting having that IP address well it starts from here so we have two to the 32 IP addresses more than four billion IP address and we can we can have

partition that IP address space, huge space, into five so-called classes. The first one is class A, class B, C, D, and E. And the IP address is that belong to this range are called class A. The ones here are called class B and so on and so forth. To be more visible, what happens here is that, okay, this is the whole IP, for her space. The first half is called Class A.

And in the remaining half, the first half of it is called class B. And the remaining, this is actually quarter of the original space, the first half is called class C and so on and so forth. So if the first bit starts with zero, it's obvious that this whole thing, this I could risk, is a class A of this, right? Because the first half starts with zero in the first position, right? And likewise, class B starts with one zero in the first two bit positions,

Class C starts with 110, Class C is 1110, Class C is 1111. So what are we doing here by partitioning this IP address space? Well class is a unit of, class is used as a unit of IP address location. Meaning, if you allocate an eyedrass from this space,

There's a certain size of the set of IP addresses. What do you mean by that? If you are allocated an IP address from class A, you're not allocated a single IP address. What happens is if the allocation is from class A space, you are given to the penny pool, I could just,

IP addresses as a group. And if you are allocated IP addresses from class B, I mean here you mean network, okay? Network is allocated in IP addresses. If you are located from the class B space, you are going to get 2 to the 16 addresses. If C, then you will get 2 to the 8. Plus D and E are the

are used for different, sorry, special purposes. For instance, class E is used for multi-class, which we'll discuss later. Class E is reserved, meaning it's not as yet, so we'll leave it at that. So there are three classes from which you can be allocated in a unique class, class A, B, and C. So this is more than, I guess, about 70 million, I think it's a lot of people who are interested in it.

So for instance, Apple got this. Originally Stanford University got this. U.S. Army got it. And so on. So the early members of the internet, I mean the guys who joined the internet in the early times, early days of the internet, all got class A. A lot of hypothesis.

Korea University which one? It has A or B or C. We are B. We are B. You remember our address starts with 163, 152. Look at the first few bits. 163, does it start with zero in the first bit position? No, because it's larger than 128. Alright? So, it starts with 1.

second position is it 1? no it's smaller than 192 so it should be 0. 1 0 so we are 1 0 plus B that means we were allocated how many IP addresses when we joined the internet? this many how many how many how many this is 64k which is six

55,536 addresses. So we have this many ID addresses. But if you turn on your computer in the university, you will not get this type of address, 163122. I'm not going to get it. What address will you get on your laptop connecting to the campus network through Wi-Fi? What do you get? - Have a good one.

- I have one side.

So, you can use the ipconfig command and see what IP address this guy has. It's 163.152.190. Sorry. This guy has... Oh, okay. So this is the IP address of this one. Because this is connected to the campus network through ethernet, it has been assigned this 163.152 address. But what about you? If you have a Windows laptop, try this and tell me.

your IP address look. What's the first number you see in the data testimonial station? Anyone? Nobody using Windows these days? IEP config, somebody please try this. IEP config slash O.

What do you see in the IPv4 address MQ? Must not be 161. Must be something like 10 dot, right? It starts with 10. So 10, what is 10? 10, okay, decimal number 10. It starts with zero, right? Does it mean that it comes from class A space? Yes, the answer is yes. But it's a very special address.

Although it comes from the class A space, 10, from here, it is given to everybody. We have 10, Yonsei University has 10, KAIST has 10, everywhere, in the whole wide world. Every network has 10. This is called private icon. You can use it privately inside your network.

but it will not work if you want to go outside. What do you mean I can browse the website from here using 10? I'm not lying. What I'm not telling you is that there is some translation from this private idea for global address. Okay? So even if you see 10. - I have something as your IP address if you do IP company.

If your IF company, if we use Linux or iOS user, it'll be translated by some machine in the computing center before your packet goes out. How can you know? Well, you go to some website, what's my IP?

is my address and it tells me that this is my address one that's true because that's really my address one any five but what about you using ten but does it tell you do it go to the what's my IP address dot com site and see what it tells you about your IP address the real IP address you must start with 160 mm

it. Yes, yes, right. Some translator lives there in the competing center. Translating this, which is private, to a real Korea University, 163. Okay? It's like community money or game money, not real money. Okay, so you have to change. But we will discuss this in, I don't know, chapter 10 or something.

transmission. All right, so in the beginning of the internet, almost everybody got Class A of this, because they didn't expect that the internet will be this huge success. They thought internet was going to be an experimental network, a research network shared by a couple of, a handful of research institutions in the US Army.

So they gave out these IP addresses in the units of 17 million. That happened in the early days of the internet. But soon they realized that was not feasible, not sustained. So class was the unit of address location. If address comes from class A, no matter what, you have to give out this many addresses. to that organization that's joining the entire community.

if your address is from class B you get this many class C to the A so that was the notion of class that was involved in the address allocations but in 1990s it became evident that this cannot go on because Most of the organizations that were joining the internet

time had more than 206 computers but less than 664 kilo so this is a typical Goldilocks problem who is Goldilocks? Korean students remember this. Three bear stories. The little girl - Yeah.

Her name is Goldie Lutz. And you know how the story goes. There are three beds. Big one, small one, middle one. And the middle one always fits her height. So she sleeps on that middle bed and she eats one of the three bowls of porridge

second one was was warm enough not cold so she has I mean this this this picture depicts that situation she always chooses the middle one in the story just like that every organization that was joining the internet chose class okay so they were given this Korean University was one nobody was as small as this or as large as this

So everybody got this address. So these addresses, 2 to the 16 addresses, were given from the class B space. So everybody was getting their arches from here. And soon it was obvious that this address space, class B's address space, would run out of the arches addresses. Because there were only 2 to the 14 blocks of this, 2 to the 14. Why only 2 to the 14? Because the size is this.

the number is 2 to the 14 if you multiply them you get 2 to the 30 why not 32 because you have 32 bits sorry but you used up two degrees of freedom already and what were they one zero that's already fixed okay so that's not yours one zero has been used up and the only degrees of freedom that you have now is 30 that's how you got only 2 to the 14 class b address blocks which means after

up to the 14 organizations can join the internet under this class structure, class full structure, sorry. So they decided that to get rid of the notion of class as the unit of address allocation. So nowadays they are located, nowadays, it used to be the case that they locate address blocks from any classes.

classes so class A, class B, class C but not sticking to this rule. Even if you have only 22 to the 8 addresses that you need you can be allocated from class A space. The size and location they are detached. They are not linked anymore. You can get allocated IP addresses from any space from here to here. From A, from E, from C. Well that used to be the case. Why I say used to be the case? Because there's no IP address left.

you ran out of it. So that's one of the reasons that you're using address 10.

I'm going to explain that in more detail later. Okay, so we are now classless. Classless, okay? The term class still stays with us, but its function has been removed. Okay, so it's not a notion that actually constrains the allocation process. Okay, now let's come back to the...

structure of the IP address. So I told you that in the early days of the internet, they allocated IP address like this, as ABC. So if you are a class A network, for instance if you are an Apple company or Stanford University, you are given an 8-bit number. That's all. You do not move IP addresses in trucks. There's a phone call and they tell you, "Hey, this This is your

This is your microdress. Anything that starts with 11 is yours. So in that case, you have 24-bit degrees of freedom. 24 degrees of freedom. Meaning you can use any number, any 24-bit number for your post-print. And the first 8-bit, which in this example is 11, refers to your network. So in case of Korea University, we have 16-bit network number, which is 160 to 165.

163.162 and anything that comes after that we can arbitrarily assign so this guy has IP config, this guy has 190 to 185 this number was assigned to this PC by our administrators so we have degrees of freedom in this part but this one is fixed.

and we will locate it just at the present.

In class C case, only 8 bits that provide you with this equivalent.

So this address structure reflects the structure of the internet itself where it is a loose federation of independent networks. Each network has a network number that everybody else knows. And inside the network, you can assign the host network.

Let me use an analogy. So, suppose Barack Obama sent this guy named Hong Gil-kong living in Arang-dong-ia. This is the address of the city. You can see that. Somehow Obama knows Korean. He writes all addresses of this, all entitled in Korean.

the only thing that is English is Korean and there's no problem with this letter to find although that letter went to the USPS US Postal System does it mean that the the workers working in the US there's no Korean the only thing they need to know is this they don't care where inside Korea this letter goes

That's the local delivery problem, not their problem. So just like that, anyone outside Korea University, as long as they know that 163.152 is Korea University, that's enough. For the tactic that has this destination address, to come here and deliver to the final destination. Because the delivery using the latter part of the host address, the host number.

that delivery is up to us. So what's inside the internet is this: the pointer to in the direction of Korea University given 163.152 in the table. Okay so 163.152 whatever institution that is, whatever organization that is, you have to go this way. So such a pointer is planted in every router inside the internet.

And that's all it needs to know to forward the packet to Korea University. Once the packet arrives in Korea University, in the computing center, they look at this number to deliver the packet here. For instance, if, say, this computer is 190 to 185, so this 190 to 185 is not necessary to be inside the internet to forward any packet that's needed to be used. They only need to know 163, 152. So they deliver the packet to Korea University.

And the rest of the delivery is up to us, our machines in South Korea University. They look at this number, 192.25. First they find this 192. This is the subnet number that we'll discuss immediately, soon. So 192.192 obviously is buildings around here, some buildings. And among those computers, under the 192 subnet, this is the guy, 185.

So that's how the packet is delivered to this guy. So this IP address reflects the internet structure light in that manner.

And you can use this who is database to which organization a particular IP address belongs. So who is? Let's try. So run this wire shock.

some...

So 163, 150 to 192, 237. You want to know who owns this site?

you know, who owns this address, 2320717731. And you can go to whois.hr, whois. You can look up the whois.hr, please. Okay, so whois.hr, and you enter this IP address, and you enter the IP address,

says? Oh, come on.

You can do this yourself. So it belongs to this company, Akama, which is a content distribution network provider. So you can immediately see where this address, particular address, was allocated to by using who it is.

yourself. Okay so we have the first crisis and we're worried about the end of internet in early 90's I guess. And so this was the first problem so they decided to get rid of this notion of classes as units of address allocation. And as

consequence we created another problem which was the routing table explosion it means that since you can now allocate a very small address space from from any class space any classes suppose you you allocated your address from class No. Okay.

Let me take another example. Suppose you are a new university and you want to connect your network to the internet and you need say, how many addresses? 2 to the 13 addresses. This many ID addresses, 2 to the 13. Obviously, Class E of this case...

provide to the 16 so it may serve this this network class you might address location organizations can give instead 32 of class C so 32 which is 2 to the 5 and this class C 5 times 2 to the 8

this way they can meet their needs the problem is that there are 32 Class C entries that must appear in the routing table so it's a single organization that's joining the internet but because of them or because we decided to allocate a bunch of Class C blocks to the single organization we have to create 32 routing table entries okay so the first block goes to this university the

second block was to that this I said the third one everyone is second one also goes to this organization so you need 32 entries but the problem is that the routing table size is already big so how many routing table size how many routing table entries do we have in today's internet it's over a million okay so it's already out there was

2006, we were threatening 942, we were threatening a million, and we are already over more than a million entries. It's not easy to route a packet by looking up this huge table. A table that has more than a million entries, you look up the table, like, I don't know,

a million times a second, because that's what happens inside the network. Can you do it? You have to be very clever in designing data structure and the algorithm. And that's not enough actually. You have to use harder acceleration. Because even the single memory read can take a while. A few tens of nanoseconds. And you have to process I don't know, 1 million or 10 million units.

per second and every packet requires a lookup of this huge table that has more than a million entries. So that's a huge problem. So what they decided in the middle of 1990s is to aggregate or compress the routing table. If you took digital design course you know how bits can be sort of

aggregated to create a very compact representation. For instance, if you have 0010 or 0000 then you can compress this as... This is "Don Care". Just like this. So those 32 address blocks that we used as an example here, these 32 address blocks

very similar values. For instance, this is from the same example, right? So the first 16 pieces are the same for all these guys, all these 32 guys. The only... Alright, so these are Class C addresses, so they have this structure.

So the first three bytes are network number, and the last eight bits, they are host number. So network number, we talk about network numbers here because inside the internet, the routers only look at your network number. Remember this example. So only network number is inspected by the routers. And these 32 guys have the same first 16 bits. only the third byte, which is the last byte of the network number,

in a few bit positions. In particular, the first three bits are all the same, in the sense that they have three zeros at the beginning. The degrees of freedom are provided by the last five bits, okay, zero zero zero zero, that's this guy, two two two zero zero zero, and zero zero zero zero one, okay, so that's going to be two two two two zero one zero, and so on and so forth. Okay.

to the 31. So from 0 to 31, 32 guys. So we can summarize this as a single entry. In a single entry, 22 to the 1, or 0, 0, 0. And then we specify that the first 19 bits, only the first 19 bits matter. What do you mean? First 16 bits, they are the same here, across

plus the next three bits. So 16 plus 3 is 19. The first 19 bits are the same. So whatever starts with this first 16 bits, and then 0, 0, 0, they all go to this university. So this is how you summarize these 32 entries into one entry. By using this notation, by using this 19, slash 19,

So this is what we did in 1990s, in the middle of 1990s. Unfortunately, Japan was earlier than us in adopting the internet, and they were running the internet by that time. We were actually, during our internet, we do not have any record of what happened in Korea. So this is from Japan. Alright? So, if this is a Japanese routing table, the same thing is, it's not a problem.

size was very very small compared to our compared to the right in public table size today it reached about 3,000 at the time and by aggregation they reduce it reduced so this is when that aggregation happened around October of 1995 and they compressed these entries you know in the way that we just described and it went down by half and it kept growing even after that

So the routing table size that we have today is a result of applying this aggregation to it. Without it we could have ended up with I don't know how many millions of entries. Tens of millions of entries. So we have compressed the routing table so that the routers can cope with the traffic coming in

into it, process as many packets at a given time, in a given time. So it is really really essential for the internet to maintain its speed as today. Alright so this was 2019, so we were approaching 800,000. I'm pretty sure there will be over 1 million nowadays. But unfortunately this is

doesn't solve this problem entirely because before we realize this problem we randomly allocated adjacent address blocks to every part of the internet so in this case the whole idea starts from observation okay so this adjacent address blocks used by a single institution single organization or this adjacent address blocks are given out to the organization

in the same geographical region. Then we can't do this. However, if one block went to Africa, the next block went to Asia, the next one to Australia, and if that happens, aggregation doesn't work. Because they all have to point to the same direction, right, the aggregated entry. But if these component blocks point to different directions, how can we summarize that into a single direction? That's impossible.

But unfortunately that was what happened before this. So we have some area of some region of IP addresses that we cannot compress enough. So we ended up more than 1 million entries today in the routing table. And that's why we need a very fast algorithm, very fast hardware in the routers today. And I asked you this question, where did your IC address at home?

from? This is the answer to that question. It came from this organization, ICARP, which stands for Internet Corporation for Assigned Names and Numbers. It's in the United States. So when the internet was freed from Department of Defense, USDOD, they created this organization, ICARP. The United States obviously wanted to maintain control over the internet by having this organization inside the United States.

Although this is a civilian organization, this whole infrastructure is still in the United States. And inside ICANN, there is this function called IANA, Internet Assigned Numbers. This is not an organization. This is a function. And IANA practically controls the Internet Allocation, although unfortunately Internet Allocation is over because the Internet is not over.

IP version for stress space is exhausted. So it happened in 2011, okay? About 15 years ago. And do we have any problems because of that? No, we don't. Because we actually anticipated this problem. We knew this problem would happen someday, okay? So what happened was that the engineers came up with a solution.

before it really happened.

Okay, so they prepared for this day and they came up with two solutions. One was IP version 6 and the other one is network address translation. This we talked about, okay? Your address here inside Korea University starts with 10 dot something. It starts with 10, right? Like this. As long as there's a translator in the computing center at the boundary of our network.

translates your local address or private address that starts with 10 to something real is ours 163 something then you can still talk to a host outside our network using 10 does something as your address because from outside you look like not 10 but 163 152 because there is a translator that works magic and then magic is based on this statistical property and

여러분은 우리 학원에 따른 학원에 대하여 전화할 수 있습니다. 그래서 스타디스틱을 골고루가 있습니다. 그래서 작은 아이디어드레스는 64K가 있고, 전화가 많은 것과 하나의 계획을 할 수 있습니다. 그래서 그 부분에 대한 소식은 없습니다. 제가 더 더 디테일에 대해서 알아볼 수 있습니다. 질문이었어요. 그러면 C부로 시작하는 것은 클래스에는 안 들어가고,

내부에서만 쓰는 클래스 AL에 해당해야 합니다. 그래서 이 클래스는 어떤 것인지에 대해 알아볼 수 있습니다.

As long as that is done at the boundary, everything is okay. Yes? So it was a stopgap kind of solution. Okay, temporary solution was designed to be a temporary solution, but unfortunately it stays with us today. It's here. Thank you.

it is not going away okay so we were that we were planning to transition to IP version 6 when it came when it comes but unfortunately that it solves most of potential problems that can be caused by IP address exhaustion so the transition to IP version 6 came very very late but gradually IP version 6 addresses are being adopted for instance if you use mobile network as

SKT, for instance, if you trace route your packet through that mobile network, it goes through routers inside SK Telecom, and you can find that their addresses are IPv6, not IPv4. You can force your packets to be IPv4, even crossing SKT, but by default it's IPv6. But anyway, so they are being deployed incrementally, and they're replacing IPv6 for Internet bit by bit by bit, but it will take very, very long.

until we see the end of our conclusion. Entirely. It will take a few decades, I'm pretty sure. So these two solutions are with us even today. And you are using it at school, at home. I mean, net. Net is being used by our network, your home network, almost everywhere. So, going back to this story. before we end. So it came from IANA.

and big chunks of IP addresses are given to so-called regional network information centers. For instance, ARIN here is for North America. This white NCC is for Europe. APNIC is Asia Pacific. AFRINIC is obviously for Africa. Latinx is obviously for Latin America. Okay, and below APNIC for instance we have national information network information centers. KRNIC is obviously our network.

Information Center in Korea. Japan has its own JPNIC. China has its own. Taiwan has its own TWNIC. Under KRNIC we have these companies and other networks, public networks like education networks and so on. For instance, I'm a KT user at home. So KT got a small subset of what KRNIC has been allocated by APNIC which in turn came from

So big chunk, smaller, smaller, smaller chunks. And one of the KT addresses I'm using. And they pay for it. IP addresses are not free. KT pays money to KRNE for the use of IP addresses. So your IP address came this way. And your home router, internet connectivity, got its IP address.

following this rule. And the rule was that, okay, if you're, if you allocated more than 80%, tell me, says the higher the organization. But this never happens today because we ran out of the IP address. There's no IP address to give you. So you have to, you have to use net. You have to use net as a translation. I think software is a more complex issue so that,

requires more time than four or five minutes. But let me just tell you what's going on. So suppose Apple got some number, 8-bit number as its network ID, and it's using 24-bits to identify some host inside that network. So with this network ID packet travels across the internet, finally arrives at Apple.

At the boundary there's a router and it examines this 24-bit number and decides where to go. Where to forward this packet. Now 2 to the 24 is a very, very big number. So it's like finding Mr. King in Seoul. A huge number of connected addresses and you have one of them. You have to find a matching interface with that I-currence. How do you do that?

get the inspiration from our own postal address structure. We never send a letter to Mr. Kim in Songbuk. We never do. We have a structure hierarchy in the address. Songbukku, Anam-dong, Oga, 126 Okay? So there is this hierarchy. Just like that we introduce hierarchy here so that we do not end up finding a single interface with the 24-bit. So that's what's going to happen. So we use some bits from the host ID position to

identify so something and this hierarchy can be recursive we can introduce more levels here if you want okay possible but in this particular example we only introduce one more level and it's just like our university in Korea University uses one level subnet you go back this this guy has ID address of 163 152 192 185 and

And this 192, this number happens to be the subnet number. So this 192nd subnet is here. And this is a member of that subnet. It's like... So 192nd subnet. And this guy is 185th member of that subnet. So when a packet arrives with this address in the competing center, the router there does not use this entire 16 bits to find a single host. It doesn't do that. It first sends the packet to 192nd subnet.

And then the router there, okay, at the entrance of that 192 subnet, looks up the routing table to find where a 100.5 is. So this is a hierarchical delivery. And subnetting allows that. So we'll discuss that in more detail next time. Okay. See you, my one. Thank you.