RC Day 2: Pair-ity

Like I said at the end of my post yesterday, my goal for today was to focus on paring. It wound up being an extremely social day; I met more people and hung out with several of the people I’d talked to yesterday, and had a lot of fun.

Yesterday when I was chatting with Ori he told me about emulators for the PDP-10. The PDP-10 was a 36-bit architecture, whereas most modern architectures are 32-bit architectures. This is an issue because a lot of computer components assume the memory will be addressable in 8-bit bytes, but 36 doesn’t divide into 8. Emulators get around this by using the parity bit in error-correcting RAM as actual data, disabling their error correcting functionality. They call this the disparity bit.

So there’s a bit of what I learned yesterday and it fits in with the punny title to this post.1 I’m not gonna stop with the pun titles until I run out of them. That will either be never or next Thursday.

Who’s That? The Mastermind

There was an excellent pairing workshop this morning run by Allison and Bill. Right before the workshop Shean and I briefly looked over the DNS server,2 then I paired off with Alex to work on an implementation of the game Mastermind. The game is a fun guessing game. Four pegs of different colors are picked and then you get ten guesses to get the combination, with each guess telling you how many answers are right and how many are the right color but in the wrong place.

We called our version Mmastermind, in honor of the tragically broken m key on my Macbook’s butterfly keyboard.3 I had a lot of fun learning how ANSI terminal colors work; it turns out that a “Bold Red” is often just an entirely different color from “Red” to get around the relatively limited set of colors (8 regular and 8 bold) a terminal has to work with.

Coffee Chats and Network Hacks

The coffee chat bot at RC pairs people off daily, so today I got to have coffee with Nathan! Thanks to my morning of pairing, that became a lunch instead of a coffee. I learned about what Nathan was working on at Recurse and about NixOS and shell configurations and a lot more. I really like the daily pairing of coffee chats; it makes every day have a bit of randomness to the interactions I’m having and mixes things up a bit. There’s also a pairing bot which I signed up for, so I’ll see how that goes tomorrow!

With a decently large group of people who expressed various interest in Montague4, I spent the rest of the afternoon pairing and working through some arbitrary stuff. This segued off into a really great in-depth set of conversations about how DNS and networking in general worked. There’s a bit of interest in starting a networking club to talk about this more!

For understanding DNS better, I’m a fan of the comic series DNSimple put together as well as James Routley’s article, Let’s hand write DNS messages. I also chatted with Sam about his super cool project to try and build isolated private networking clusters; we talked a bit about the Data Link and Network layers of networking and how traffic is ultimately routed via autonomous systems. I don’t have nearly as solid of a grasp on BGP as I do DNS, so it was a lot of fun to run through this and find where I’m missing a full understanding.

DNS is WEIRD

Bernardo and I worked out how to make the DNS server not crash when it received EDNS OPT records by adding support for OPT’s weird recycling of the RRType class field. The code we put together didn’t feel quite right to either of us; because the new value technically isn’t a class, putting it in the class field feels wrong, but that’s also effectively what the spec is already doing. Bernardo suggested making class itself into an enum, which I also like, and might look into more tomorrow.

Bernardo also pointed out there might be even more pseudo-RRs5 like this. I’m entirely unsure how to confirm that we’re handling all the appropriate edge cases!

After we did this, we got sidetracked noticing that a query for ALL records was being rejected by a handrolled request we built but not by a (seemingly identical) request from dig. We opened up Wireshark to trace down what was going on and after a few dead ends realized that dig would recreate the request over TCP when it was truncated and rejected over UDP. Apparently, some DNS servers will serve a request for ALL records, but only when it’s coming over TCP. Presumably this is a preventative measure for amplification attacks.

Even more interesting, not all the servers we tried behaved the same way; Quad9 and Google both behaved like this (with different sets of records included in the responses, though), but Cloudflare DNS refused an ALL record request even coming over TCP directly. Clearly I still have a lot of stuff I need a better understanding of to be capable of this project.

At the end of the day there were a bunch of non-technical presentations I thoroughly enjoyed. Some of the themes covered included the history of Pong, the beauty of Arabic cursive and calligraphy, and how to poop in the woods.

Overall it was a wonderful second day at RC. I look forward to tomorrow!

  1. I also played a card game involving pairs yesterday, but I’m not gonna do two punny leads. Unless you’re the kind of person who reads the footnotes. ↩︎

  2. I keep debating whether to call it Montague or not in these posts; I haven’t been using that name much recently so maybe that’s why I’m avoiding it here. An A record by any other name would smell as sweet, but maybe a different server name would be less silly. ↩︎

  3. I plan on getting it fixed but I’m not sure what I’ll do without a laptop. ↩︎

  4. And now I am using the name. I bet that’s confusing for people who don’t read footnotes. ↩︎

  5. That’s not meant to be mean to OPT records; the RFC literally calls them pseudo-RRs. ↩︎