Archive for the ‘System Administrator Articles’ Category

tcpdump for Dummies

Table of contents Introduction tcpdump uses Invocation Simple filtering Reading tcpdump‘s output Invocation continued Choosing an interface Turning off name resolution Limiting number of packets to intercept Saving captured data Changing packet size in the capture file Reading from capture file Looking into packets Seeing Ethernet header for each packet Controlling time stamp Controlling verbosity […]

Reverse SSH tunnel or connecting to computer behind NAT router

Introduction Few days ago I encountered a problem. How do you connect to a computer behind NAT router? Any NAT router is also a firewall. Sometimes you do have access to firewall configuration and can set up port forwarding. Yet often it is complicated and even impossible. Common situation is when you want to connect […]

SMP affinity and proper interrupt handling in Linux

Introduction Hardware interrupts has always been expensive. Somehow these small pieces of software consume so much CPU power and hardware and software engineers has always been trying to change this state of affairs. Some significant progress has been made. Still hardware interrupts consume lots of CPU power. You will rarely see effects of interrupt handling […]

Useful Linux Networking Commands

This article describes most useful Linux networking commands, as simple as it sounds. The truth is that I am writing this article more for myself. I am rarely doing complex networking configurations. As a result, when I have to configure something, I often forget commands and their syntax. Often it takes hours to find out […]