Having fun with unusual IPv4 formats

Did you know that “2130706433” is a valid IPv4 address, and pinging it from major OSes will yield a positive result? Let’s look into how it works.

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Linux system as an IXP router

While it is possible to use a Linux based router in an internet exchange setting, there are some tweaks one has to make in order to not cause any trouble.

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DHCP server on a /32 subnet

How to force a DHCP server to hand over /32s, while running on a different /32 subnet.

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ECMP problems between two systems

Solving a tricky problem with ECMP between two machines, where one system refused to balance connections at random intervals.

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Looking Glass Collection

A collection of looking glasses of various ISPs

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Retaking control of your network: Part 2

Computer networks are becoming increasingly complex with more and more devices connected each day. Gaining network visibility is absolutely crucial to ensure your traffic flows smoothly and transit costs are kept low. In this mini-series I will show you how to set-up sFlow sampling on Linux, aggregate the data and finally present it in flashy graphs.

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Retaking control of your network: Part 1

Computer networks are becoming increasingly complex with more and more devices connected each day. Gaining network visibility is absolutely crucial to ensure your traffic flows smoothly and transit costs are kept low. In this mini-series I will show you how to set-up sFlow sampling on Linux, aggregate the data and finally present it in flashy graphs.

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SSH jumping through multiple jump hosts

The standard OpenSSH SSH client accepts the argument -J to allow users to utilize a jump host/jump box.

What I recently discovered (and isn’t immediately obvious from the documentation) is that you can actually specify multiple jump hosts – separated by a comma – and the SSH client will jump through each single one in order to reach the target.

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dig TXT whoami.ds.akahelp.net.

Core Backbone/AS33891 BGP Action Communities

A list of available action BGP communities for Core Backbone, AS33891.

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