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Tag: design

Effectiveness – Network Truths, Principles and Fallacies

Effectiveness – Network Truths, Principles and Fallacies

I gave a 13-minute talk to the Irish Network Operators Group (INOG) recently. In this 13-minute video I argue that you can become more effective, and happier, by standing back and reflecting on how you work, leveraging existing truths, fallacies and principles. I introduce The twelve networking truths and the 8 Fallacies of Distributed Computing. I then describe a handful of my own learnings and fancy terms like Chestertons Fence and the Gordian Knot. Check out the video folks, I’d love your feedback.

SPAN Scaling Challenge

SPAN Scaling Challenge

I’m facing a mini scaling challenge with Cisco SPAN (Switched Port ANalyzer) session and thought it would be good to share it with you fine folk. SPAN Challenge A 3750X switch is currently SPAN-ing a 10Gbps interface to a 1Gbps egress port. A server is directly attached and is using dump cap to capture a subset (5%) of the overall traffic for analysis. The 10G link under-utilised, but is running close to the 1Gbps traffic limit in the Rx direction. Tx traffic is very…

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Hardware – What’s the ‘holdup’?

Hardware – What’s the ‘holdup’?

This post discusses power supply ‘holdup’, and how it can impact network or server hardware uptime. The holdup time or ‘output holdup time’ is the length of time that a given power supply can maintain output power to the switch or server after it’s input power supply has been cut. The dependent host will shut down if the power supply isn’t restored to the PSU before the hold-up time expires. I like to think of holdup time as a power…

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Planning projects instead of burning benjamins

Planning projects instead of burning benjamins

Engineers are often unstuck by poor planning and get hit with large financial penalties as a result. Projects can become mired in delays and complications due to unforeseen costs and expenses. There are some unavoidable bumps in the road, but most could be foreseen and eliminated in advance. I want to share a few tips based on some experiences I’ve had over the years.

Does config automation demand inflexiblity?

Does config automation demand inflexiblity?

Imagine you’ve just designed and deployed a data center. It was hell but you are smiling. Your design is homogenous, simple and elegant. A greenfield datacenter full of shiny, identical network devices. Because the design was so consistent and repeatable you scripted the generation of the device configurations without too much hassle. This is a network with an easily ‘provisioned’ network configuration. But day-one provisioning is only one part of the puzzle.  The real prize is a centrally ‘controlled’ network configuration, where all config…

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Airflow is important – terminology is key

Airflow is important – terminology is key

Data center cooling and large chassis As a network engineer you need to be aware of the data-center environment where your chosen device will be deployed.  A huge wedge of the cost of running a datacenter are spent trying to keep it cool.  So preserving hot-aisle and cold-aisle airflow containment is a big deal for your data-center manager.  But it’s pretty easy to order hardware that messes with the datacenter airflow.  You need to watch for context and read the…

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My 10G switch goes up to 11

My 10G switch goes up to 11

Stealing bits Nailing down the true speed of a 10GbE link can be tricky. For a start you to define ‘speed’ and ‘capacity’. Ivan Pepelnjak offers a nice summary in this post. Then there are little surprises. A former colleague of mine Fred Westermark first introduced me to the Ethernet interframe gap. I had never heard of this before and felt a bit cheated to be honest.  Since when do ‘bits’ need a rest. Pfff.

Network design – scale without busting your budget

Network design – scale without busting your budget

Rapid growth I read an article by Greg Ferro about twenty-percent-growth recently.  Greg makes the point that most network growth forecasts are grossly overoptimistic.   However, my experience in the service provider world is that ‘the business’ underestimates growth in most cases. Network engineers have a fiscal responsibility not to gold-plate their network designs; network gear is just too damn expensive.  But you can over-optimise for cost.  It is incredibly frustrating to overhaul and scale-up a network within a year of the initial…

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