Tag: hardware

  • Strain relief

    I’ve got a problem with sagging cables, and I’ve got a simple solution. Examine the side-by-side images below which show the same fiber connection between a switch and a firewall. The image on the left shows a sagging cable which crosses in front of the switch in the rack unit just below it. As you may know, this cabling install…

  • Programmable ASICs

    I love learning about network hardware, but I’ve always found it difficult to get detailed information on ASICS. We had a great presentation from Dave Zacks on the Cisco 3850 programmable ASIC at the Cisco Live Europe Tech Field Day event.

  • Network config backups – just the beginning

    An emergency switch replacement can ruin your day. However, having network config backups is not enough. Restoring full service may not be as easy as just copying the running configuration from your RANCID CVS repo, or your colleagues hard drive. Restoring the ‘identity’ of your original switch is a multi-step and somewhat complicated process.

  • Hardware – Equalization and Pre-emphasis

    Before we look at equalization and pre-emphasis, we should examine some fundamentals of waves and signals. A perfect square wave is a really useful way of representing a waveform in the time-domain, but it’s not the only way of looking at the signal.The name ‘time-domain’ may be new but the view is familiar to us all,…

  • Hardware – Differential Signaling

    I’m planning a series of blog posts that delve deeper into the way networking hardware works. This started with an idea for a single blog post on PHY-chips but I found that there were too many fundamental concepts that I was ‘assuming’ were already known. I’m not an electronics expert, but I hope that I…

  • 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…

  • 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…

  • 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…

  • Video – 10G Fiber Transceivers – Network Sherpa

    I’ve just recorded a quick video about 10Gbps fiber transceivers, There’s a first for everything I guess.  It’s a cheat sheet which describes the different transceivers, where they’re commonly found and the connectors you use. I’d love to hear your take on the video.  Too long… too short, music too cheesy (yeah I know!), etc.…

  • TCAM-based forwarding engines

    Overview Ternary Content Addressable Memory, or TCAM,  is a critical component of a modern router. It is a powerful and fast hardware lookup engine for IP Prefixes.  It is also complex, expensive and power hungry.  Not surprisingly, there never seems to be never enough on whatever system you use. TCAM has historically been used to…