Year: 2017

Network Traffic Control (QOS)

OpenWrt, which is a Linux distribution for embedded devices, website has a really handy HowTo on Network Traffic Control (QOS).

Traffic Control is the umbrella term for packet prioritizing, traffic shaping, bandwidth limiting, AQM (Active Queue Management), QoS (Quality of Service), etc. This HowTo will help you understand and set up traffic control on your router. It is one strategy to address problems caused by Network congestion.

It covers the tc (traffic control) and iptables commands, and much more.

Containers are not a real thing!

Jessie Frazelle reiterates her point on containers in the blog post “Setting the Record Straight: containers vs. Zones vs. Jails vs. VMs“:

The Design of Solaris Zones, BSD Jails, VMs and containers are very different.
Solaris Zones, BSD Jails, and VMs are first class concepts. This is clear from the Solaris Zone Design Spec and the BSD Jails Handbook. I hope it can go without saying that VMs are very much a first class object without me having to link you somewhere :P.

Containers on the other hand are not real things.

A “container” is just a term people use to describe a combination of Linux namespaces and cgroups. Linux namespaces and cgroups ARE first class objects. NOT containers.

 

Wireshark Layer 2-3 pcap Analysis w/ Challenges (CCNP SWITCH)

Johannes Weber, a networking and security professional, has done something really cool while preparing for his CCNP SWITCH exam.  He has built a lab with some networking equipment, configured it all, and captured network traffic, featuring a variety of level 2 and 3 protocols.  He has published his setup, the captured traffic, and a variety of challenges, that helped him to prepare, and which can help others.

While preparing for my CCNP SWITCH exam I built a laboratory with 4 switches, 3 routers and 2 workstations in order to test almost all layer 2/3 protocols that are related to network management traffic. And because “PCAP or it didn’t happen” I captured 22 of these protocols to further investigate them with Wireshark. Oh oh, I remember the good old times where I merely used unmanaged layer 2 switches. 😉

In this blogpost I am publishing the captured pcap file with all of these 22 protocols. I am further listing 45 CHALLENGES as an exercise for the reader. Feel free to download the pcap and to test your protocol skills with Wireshark! Use the comment section below for posting your answers.

Of course I am running my lab fully dual-stacked, i.e., with IPv6 and legacy IP.

I think these are great for several reasons:

  • A feature-rich and complete networking setup, which is not easily available to everyone.
  • A fixed set of data (captured network traffic).
  • Plenty of very specific, testable, and verifiable questions.
  • Overall, very helpful resource from an experience professional, for anybody who wants to know about networks.
  • Overall, a great set of questions and challenges for those interviewing networking candidates.

The lab setup includes the following:

  • 1x Cisco Catalyst 2960, (C2960-LANBASEK9-M), Version 15.0(2)SE9
  • 2x Cisco Catalyst 2950, (C2950-I6K2L2Q4-M), Version 12.1(22)EA14
  • 1x Cisco Catalast 3560, (C3560-IPSERVICESK9-M), Version 12.2(55)SE10
  • 3x Cisco Router 2811, (C2800NM-ADVENTERPRISEK9-M), Version 15.1(4)M9
  • 2x old Notebooks, Dell or somewhat, running either Ubuntu or Knoppix Linux

Personally, I am not very involved with networks these days.  But even for more me the above setup serves as a reminder of how complex underlying technology infrastructure has got in recent years – hardware, software, protocols, and all.

WordPress Plugin : Image Processing Queue

As described in “Introducing WP Image Processing Queue – On‑the‑Fly Image Processing Done Right“, Image Processing Queue plugin tries to solve several issues with On-The-Fly Image Processing (OTFIP) in WordPress.  Some of the things that it improves are:

  • Response times for pages with non-yet generated thumbnails.
  • Server CPU spikes for pages which use a lot of images on sites with a lot of configured thumbnail sizes (49? really? WOW! I don’t think I’ve seen more than 10 in the wild, which is still a lot).
  • Server disk space issues caused by removed images and leftover thumbnails.

This is a very useful direction and I hope all the necessary bits will make it into the WordPress core.  But even for those who don’t use WordPress, the whole discussion and implementation are a handy reference.

PHPUnit Snapshot Assertions – a way to test without writing actual test cases

phpunit-snapshot-assertions – is an interesting addition to the PHPUnit assertions which allows testing against previously created snapshots.  This is particularly useful for testing the outputs of API end-points, format conversion functions, and the like.  Instead of testing the actual functionality, these assertions allow to compare the output of the current test run with the known good output of a previously created snapshot.

This works well for generic text, but even better for widely used formats like JSON and XML, where, in case of a failed assertion, a meaningful difference can be provided.

Here is a blog post providing some more details on philosophy and methodology.