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 is a violation of the 167th rule of networking: Thou shalt contain your cables to your own rack unit and shalt not, under any circumstances,…
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.
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.
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, you have amplitude on the vertical axis and time you have time on the horizontal scale. Ideal square waves need infinite bandwidth The square wave…
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 can explain just enough fundamentals to help explain the bigger picture. The first topic I want to cover is called differential signaling. Differential signaling is…
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…
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.
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…
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. All constructive feedback is welcomed.
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 perform hardware-table lookups of Access-list, Netflow or QoS tables in routers and switches. Most of these implementations from your favorite brand-name vendors use one…