Warning this blog post contains a tiny bit of boolean logic. Don’t be afraid. Let’s explore the eXclusive-OR (XOR) logic function, another hidden gem that powers computer and network systems. XOR is a binary logical operation with some very special properties. You’ll find XOR hiding under the covers of most communications systems. The goal of this post is to tell you why XOR is so special and so heavily used.
A few weeks back I posted about my experience using VirtualBox to create running Arista vEOS instances. I loved how VirtualBox made is so easy to create VMs. However it seemed unwieldy and error prone to rely upon the VirtualBox console to attach each vEOS interface to a particular LAN segment. My last post explored using the CLI to create these mappings. I had planned to generate topologies using a script to create the appropriate vboxmanage commands at some later date….
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…
A few months back I wrote a post about checklists, and promised to follow up with a few of my own. Here is my first attempt at a checklist, trying to address the common pitfalls I see when people are making network changes. I’m not sure I follow all the guidance in the ‘Checklist Manifesto’ but here goes.
I’ve wanted to check out Arista EOS for a while, but didn’t have access to the hardware. I recently learned that Arista had made EOS available as a virtual machine. Arista call this vEOS. By installing the free VirtualBox hypervisor I could get vEOS running on my MacBook. It sounded a bit too easy, but to be fair the process is really well documented. Before I go further I should say that I obtained my copy of vEOS from my…
This post is a short one, but hopefully still valuable. I spent 30 minutes troubleshooting a flapping switch port in the lab this week. I was attaching a headless test device to a 3750G and I couldn’t see the status of the NIC from the tester’s perspective. So one crash cart and a bit of port-swapping later, I found the problem. It was a dodgy switch port and swapping to another port (with identicial config) solved the issue. Then it…
It’s time for another video. This time I’m covering some useful tools for handling fiber cleaning and testing in the datacenter.
Sometimes it’s best not to trust network vendor datasheets. Nothing quite beats a controlled test of a network device in your lab with your config and your required features. But if you want to load test multiple ports on your 10G device-under-test (or DUT), then things can get very expensive, very fast. In this post I’ll show a test topology that will help you turn 10Gbps of test traffic into 640Gbps or more.
Getting Zen ‘Zen and the art of motorcycle maintenance‘ by Robert Pirsig is a modern classic. When I first read this book I didn’t quite get the zen I was looking for. But then again maybe I was trying too hard which isn’t very zen-like. It is a wonderful book and although I missed many of the metaphors I gleaned some solid advice on how to enjoy my work. I think Pirsig’s motorcycle maintenance tips can help us in our…
MTU mismatches are the primary reason an OSPF adjacency becomes stuck in the EXSTART state. After hellos are exchanged and the routers become neighbors, each OSPF speaker advertises the IP MTU of it’s local interface in a Data Base Description (DBD) LSA. If there is a mismatch you’ll probably just adjust the configuration to be identical on both ends of the link and be done. However, when you try to peer two OSPF routers with different network operating systems, things…