Category: Linux (page 1 of 2)

DHCP server on a /32 subnet

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

Read more →

ECMP problems between two systems

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

Read more →

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.

Read more →

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.

Read more →

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.

Read more →

ECMP on Linux

During a new server deployment I’ve come across the need to use ECMP on Linux. Turns out it’s actually really simple to configure. Read more →

Bird Unreachable Routes on multihop BGP Sessions

In the past few months, quite a few people have asked me this question: “I bought a VPS from provider X, turned up a BGP session with them and my routes are all marked unreachable”. Today’s post will hopefully shed some light on what causes this phenomenon and how to deal with it.

Read more →

Backing up OVH Public Cloud instances using snapshots

OVH Public Cloud platform is based on OpenStack software. As such, it has an API using which many procedures can be automated. Today I will be showing how to automatically create whole server backups using snapshots.

Read more →

Postfix: Routing outgoing email based on sender domain

I was in a situation where I needed to implement a mail routing policy: Outgoing email from a specific domain gets routed through a relay (eg. Amazon SES) and all other goes directly.

Read more →

Compiling nginx with PageSpeed and naxsi

Today we are going to compile nginx web server with naxsi WAF (Web Application Firewall), Google PageSpeed modules and HTTP/2 support.

Read more →