Tcp ephemeral ports rdc11/20/2023 Now, we’re close to 30 billion and we expect there to be in 2025, about 75 billion devices. And I think last time I recorded this, there were about eight billion devices the Internet. If that’s the world you live in, more than four billion is an insane amount. When the Internet was designed, they thought maybe in every large city there might be one computer. And we did that because IPv4 really only has four billion usable addresses and four billion does sound like a large number. What we did was we moved any device that is capable on its own to run IPv6 to IPv6. There has been a lot of shuffling on the back end, but for most consumers, they never know. But since so many devices now are ready for IPv6, we have really mostly avoided running out. You may have heard 8, 10 years ago that we’re running out of IPv4 addresses and that is technically true. But because it has a very limited address space, we are moving much faster towards IPv6 and most of these changes are something that is happening on the back end. Up till a few years ago, IPv4 was still the most commonly used protocol on the Internet. And because of all these flaws, we then added a bunch of protocols to make sure that we have reliable traffic and that we have secure traffic. So for that, we design the TCP protocol because the original IPv4 by itself, doesn’t guarantee delivery, it doesn’t ensure proper sequencing, it doesn’t prevent us from delivering the same data twice. Since it is connectionless, it is just like UDP, but there is no delivery confirmation, there’s no guarantees. So IPv4 for inherently is a connectionless protocol that is used for packet switching networks. ![]() But then again, the use case and how they were planning to use the network back then is completely different from what we do today. Security should always be part of the design process and never something we add as an afterthought later. And with anything else where you add something later, it is inherently not as secure as if it was designed in. That is why many of the protocols we use now does not have security designed in, it is something that we add to, we bolt it on. And since that network was closed and it was secured, security was not built into any of the protocols. DARPA– Defense Advanced Research Projects Agency. The ARPANet was developed in the 1970s on a secure, closed network. And ARPANet is what later became the Internet. Which is really not that long ago, but it is also very, very long ago. They were first deployed in production in the ARPANET in 1983. Now let’s look at something we haven’t talked so much about yet, IP addresses. To make it a 64 bit address, we add the FF:FE between the organization identifier and the device identifier, and this is only used on 48 bit addresses, any newer networking card will have a 64 bit address. If you look over here on the right, you can see we have a unique identifier for the organization in a 48 bit address, 58, 8D, 09, then we have the unique ID for the device, A5, 54, BA. That effectively makes it a 64 bit address and IPv6 can use that. So if our networking card is a little older and it has a 48 bit address, what IPv6 does, is it adds FF:FE in the middle of the address. I also briefly mentioned that with IPv6, they can only use the 64 bit Mac addresses. We have many more devices, so we need much more address space. ![]() ![]() Here again, the same first 24 bits are manufacturer ID, the last 40 bits, other device, unique ID. So to make sure we did not run out of unique addresses for the last half of the MAC address, we added UI or MAC-64 addresses. No one had ever predicted the Internet would be as popular as it is. And here we ran into some of the same problems that we had with IP addresses. The original design was EUI or MAC-48, meaning it is a 48 bit hexadecimal address where the first half is the manufacturer ID and the last half is the device ID. We have already talked about MAC addresses a little, how they are burned in addresses, they are supposed to be a unique identifier on the network and they’re really, really easy to spoof. In this lecture and the next couple of lectures, we’re going to be talking about IP addresses, MAC addresses and ports so we can ensure that what we send over the Internet actually reaches the right destination.
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