tcp/ip

9 Articles

The IPV4 We Didn’t Get

March 16, 2026 by 24 Comments

If you have ever read science fiction, you’ve probably seen “alternate history” stories. You know, where Europeans didn’t discover the New World until the 19th century, or the ancient Egyptians stumbled upon electricity. Maybe those things happened in an alternate universe. [BillPG] has an alternate history tale for us that imagines IPv6 was shot down and a protocol called IPv4x became prominent instead.

The key idea is that in 1993, the IP-Next-Generation working group could have decided that any solution that would break the existing network wouldn’t work. There is precedent. Stereo records play on mono players and vice versa. Color TV signals play on black and white sets just as well as black and white signals play on color TVs. It would have made perfect sense.

How could this be? The idea was to make everyone who “owns” an IPv4 address the stewards of a 96-bit sub-address block. IPv4x-aware equipment extracts the entire 128-bit address. IPv4-only equipment routes the packet to the controlling IPv4 address. Wasteful? Sure. Most people don’t need 79 octillion addresses. But if everyone has that many, then why not?

The fictional timeline has DNS and DHCP, along with dial-up stacks, changing to accommodate the new addresses. Again, you had to assume some parts of the network were still IPv4-only. DNS would return both addresses, and it was up to you to pick the IPv4x address if you understood it.

Your ISP would probably not offer you the entire extra space. A regional router could handle all traffic for your neighborhood and then direct it to your specific 128-bit address or your pool of addresses, if you have multiple devices. No need for NAT to hide your devices, nor strange router configurations to punch traffic through.

Of course, back in the real world, we have two incompatible systems: IPv4 and IPv6. IPv6 adoption has been slow and painful. We wondered why [BillPG] wrote about this future that never was. Turns out, he’s proposed a gateway that IPv6 hosts can provide to allow access from IPv4-only networks. Pretty sneaky, but we can admire it. If reading all this makes you wonder what happened to IPv5, we wondered that, too.

QUIC! Jump To User Space!

October 10, 2025 by 18 Comments

Everyone knows that Weird Al lampooned computers in a famous parody song (It’s All About the Pentiums). But if you want more hardcore (including more hardcore language, so if you are offended by rap music-style explicit lyrics, maybe don’t look this up), you probably want “Kill Dash 9” by Monzy. There’s a line in that song about “You thought the seven-layer model referred to a burrito.” In fact, it refers to how networking applications operate, and it is so ingrained that you don’t even hear about it much these days. But as [Codemia] points out, QUIC aims to disrupt the model, and for good reason.

Historically, your application (at layer 7) interacts with the network through other layers like the presentation layer and session layer. At layer 4, though, there is the transport layer where two names come into play: TCP and UDP. Generally, UDP is useful where you want to send data and you don’t expect the system to do much. Data might show up at its destination. Or not. Or it might show up multiple times. It might show up in the wrong order. TCP solves all that, but you have little control over how it does that.

When things are congested, there are different strategies TCP can use, but changing them can be difficult. That’s where QUIC comes in. It is like a user-space TCP layer built over a UDP transport. There are a lot of advantages to that, and if you want to know more, or even just want a good overview of network congestion control mitigations, check the post out.

If you want to know more about congestion control, catch a wave.

A Month Without IPV4 Is Like A Month Without…

December 3, 2024 by 91 Comments

Recently, there was a Mastodon post from [nixCraft] challenging people to drop their NAT routers for the month of November and use only IPv6. What would it be like to experience “No NAT November?” [Alex Haydock] decided to find out.

What did he learn? You’d imagine he’d either wholeheartedly embrace IPv6 or stagger back in and warn everyone not to mess with their configuration. Instead, he recommends you go IPv6 mostly. He notes he is only talking about a home network, not necessarily networks for a big company or an Internet carrier. That’s a different topic.

IPv6 has been around since 1998, but it has been slow to catch on. However, OS support seems universal at this point. [Alex] was able to easily switch on IPv6 only using Windows, macOS, and several Linux flavors. He didn’t use any Android devices, but they should be OK. His iOS phones were fine.

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Ethernet From First Principles

November 16, 2024 by 24 Comments

For someone programming in a high-level language like Python, or even for people who interact primarily with their operating system and the software running on it, it can seem like the computer hardware is largely divorced from the work. Yes, the computer has to be physically present to do something like write a Hackaday article, but most of us will not understand the Assembly language, machine code, or transistor layout well enough to build up to what makes a browser run. [Francis Stokes] is a different breed, though, continually probing these mysterious low-level regions of our computerized world where he was recently able to send an Ethernet packet from scratch.

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Tunneling TCP By File Server

June 4, 2024 by 15 Comments

You want to pass TCP traffic from one computer to another, but there’s a doggone firewall in the way. Can they both see a shared file? Turns out, that’s all you need. Well, that and some software from [fiddyschmitt].

If you think about it, it makes sense. Unix treats most things as a file, so it is pretty easy to listen on a local TCP port and dump the data into a shared file. The other side reads the file and dumps the same data to the desired TCP port on its side. Another file handles data in the other direction. Of course, the details are a bit more than that, but that’s the basic idea.

Performance isn’t going to be wonderful, and the files keep growing until the program detects that they are bigger than 10 megabytes. When that happens, the program purges the file.

The code is written in C# and there are binaries for Windows and Linux on the release page. The examples show using shared files via Windows share and RDP, but we imagine any sort of filesystem that both computers can see would work. Having your traffic stuffed into a shared file is probably not great for security but, you know, you are already jumping a firewall, so…

Of course, no firewall can beat an air gap. Unless you can control the fans or an LED.

MS-DOS Meets The Fediverse

August 9, 2023 by 30 Comments

By now, most Windows users are set up with decently functional machines running Windows 10 or 11. Of course there are a few legacy machines still lagging behind on Windows 7 or 8 and plenty of computers in industrial settings running ancient proprietary software on Windows XP. But only the most hardcore of IBM PC users are still running DOS, and if you have eschewed things like Unix for this command-line operating system this long you might want to try using it to get online in the Fediverse with Mastodon.

The first step is getting DOS 6.22, the most recent version released in 1994, set up with all the drivers and software needed to access the Internet. At the time of its release there were many networking options so the operating system didn’t include these tools by default. [Stephen] first sets up an emulated NE2000-compatible networking card and then installs the entire TCP/IP stack and then gets his virtual machine set up with an IP address.

With a working Internet connection set up, the next step on the path of exploring federated social media is to install DOStodon (although we might have favored the name “MastoDOS”) which is a Mastodon client specifically built for MS-DOS by [SuperIlu]. There are pre-compiled packages available on its GitHub page for easy installation in DOS but the source code is available there as well. And, if this is your first time hearing about the Fediverse, it is mostly an alternative to centralized social media like Facebook and Reddit but the decentralization isn’t without its downsides.

Network Programming

May 22, 2023 by 13 Comments

If you want a book on network programming, there are a few classic choices. [Comer’s] TCP/IP books are a great reference but sometimes is too low level. “Unix Networking Programming” by [Stevens] is the usual choice, but it is getting a little long in the tooth, as well. Now we have “Beej’s Guide to Network Programming Using Internet Sockets.” While the title doesn’t exactly roll off the tongue, the content is right on and fresh. Best part? You can read it now in your browser or in PDF format.

All the topics you’d expect are there in ten chapters. Of course, there’s the obligatory description of what a socket is and the types of sockets you commonly encounter. Then there’s coverage of addressing and portability. There’s even a section on IPV6.

Continue reading “Network Programming” →