Author Archives: Lasse Karstensen

Announcing libvmod-tcp: Adjust Varnish congestion control algorithm.

I’ve uploaded my new TCP VMOD for Varnish 4 to github, you can find it here: http://github.com/lkarsten/libvmod-tcp. This VMOD allows you to get the estimated client socket round trip time, and then let you change the TCP connection’s congestion control … Continue reading

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Disable Spotify song change notification in Debian Linux

Recently Spotify started sending notifications to the desktop on song change. This is unnecessarily annoying and breaks my flow, so it had to go. (and since I usually just listen to the same playlists anyway, I’m very well aware what … Continue reading

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What happened to ban.url in Varnish 4.0?

tl;dr; when using Varnish 4 and bans via varnishadm, instead of “ban.url EXPRESSION”, use “ban req.url ~ EXPRESSION”. In Varnish 3.0 we had the ban.url command in the varnishadm CLI. This was a shortcut function expanding to the a bit cryptic (but powerful) … Continue reading

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Converting a Varnish 3.0 VMOD to 4.0

So we’re getting closer to releasing the first proper 4.0 version of Varnish Cache. One of the things we need to fix is to get all the vmod writers to make sure their vmod works with the new version. Here … Continue reading

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DNS RBL test address for development

If you are writing code that checks a DNS real-time blockhole list (RBL), it looks like 127.0.0.2 is the standard address that is always in the black/white -list. This is probably know for most sysadmins/security people and whatnot, but wasn’t … Continue reading

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Varnish and Ghost blogging software

So there is a new shiny blogging platform out called Ghost. Looks pretty good to me. If you want to run it behind Varnish, you’ll soon notice it has the usual problem of setting session cookies everywhere leading to 0% … Continue reading

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GSM A5/1 rainbow tables in Oslo, Norway

The A5/1 encryption algorithm used in (traditional) GSM networks were proven to be breakable by brute force back in 2009/2010. This means that GSM calls can be intercepted, decoded and listened to by anyone. (SMS also, but that is a … Continue reading

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Building a Varnish VMOD on Debian

From the tutorials department, here are some quick notes on how to install a Varnish VMOD from source. This is slightly complicated because Varnish demands that a VMOD must be built against the same git commit (or release) as the … Continue reading

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Setting client.ip in Varnish VCL with libvmod-ipcast

I’ve written a new Varnish 3.0 VMOD called ipcast. It has a single function; ipcast.clientip(ipstring) which sets the internal Varnish variable client.ip to whatever IPv4/IPv6 address you give as the argument. You need this if you want to do ACL checks … Continue reading

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libvmod-cookie; simpler cookie handling in Varnish VCL

I’ve written a Varnish module (VMOD) to simplify handling of HTTP cookies in Varnish VCL. In essence it does the usual stuff you’d usually do with regular expressions, but with much simpler syntax and readability. It works by parsing the … Continue reading

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