• Improving Tundra's speed & code quality

    Over the course of the past month, I have released a multitude of new versions of Tundra, an open-source NAT64/CLAT/SIIT translator for Linux operating entirely in user-space. The versions from 4.1.6 up to 5.0.1 improved speed, memory efficiency, security and last but not least, the overall code quality of the whole translation engine, which was rewritten from the ground up. In this blog post, I would like to present the most important improvements, outline some of the thought processes I had while making them and point out some interesting traits of the rewritten parts of the program.

  • An analysis of Kaktus Dobíječka time circumstances

    Kaktus, a Czech MVNO, periodically (twice a month in most cases) organizes an happy hour event called Dobíječka, during which everyone gets their prepaid credit top-ups between 200 and 500 CZK doubled. These events are not scheduled, so one needs to be on the lookout for them, and are announced usually one or two hours before they start (among other places) on Kaktus’s website – on the “Novinky z Květináče” (“News from the flowerpot”) page to be exact. Upon closer inspection, I noticed that the announcements are written in a fairly homogeneous format, and therefore programatically processable without too much of a hassle.

  • Clamping TCP MSS using iptables

    Some time ago, I was dealing with an interesting problem – certain programs running inside a QEMU/KVM virtual machine with Linux as the guest OS were either not able to connect to certain Internet hosts at all, or were able to connect only after numerous timeouts or manual retries. Notably, the dnf and pip package managers were exhibiting this weird behaviour, whereas web browsers were not. In addition, this problem seemed to be present only when the host was connected to a VPN.

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