Category: 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…

  • Getting started with Network Packet Generators

    A friend of mine has just ordered a shiny new packet generator for his network lab. I’ve spent some time working as a QA engineer in a network lab and wanted to share some advice. You can purchase stateful and stateless packet generators from major vendors like Spirent, IXIA or Agilent. If you just need…

  • Does your Wave2 AP need NBase-T?

    Cisco recently launched the 2800 and 3800 series 802.11ac wave-2 access points. The 3800 Datasheet quotes a theoretical maximum throughput of 5.2Gbps when operating in Dual 5GHz radio mode (2 x 2.6Gbps). If you ran two cables to your AP you could use the second ethernet port to create a 2 x 1Gbps LAG. However there is…

  • 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.

  • East West Segmentation With ACI

      East/west segmentation is required in the data center to protect backend networks from each other. Segmentation is often implemented using ACLs between VLANS on your core switch. The ACLS are maintained by network or security engineers but define the flows permitted between hosts or host classes.

  • Link Utilisation Varies By Packet Size

    I said to a colleague recently, “you can’t get 100% link utilisation on an Ethernet link”. When I tried to explain myself I wished I could link to a simple blog post with a nice graph. So here’s a quick blog post with a nice graph. I have talked a little about link speed in…

  • The many 'modes' of multimode

    Fiber types are differentiated as multimode or single mode. Single mode was always easy for me to understand but I could never quite understand what ‘multimode’ actually meant. I’m written some notes for myself on this topic that I thought I’d share. I’m sure some physicists will have an allergic reaction to my take, but I’m happy…

  • Packet pushers podcast – Hardware Resources

    It’s been quite a while since I’ve posted here but I wanted to highlight some work I’ve been doing with Greg Ferro and Simon Chatterjee on the Packet Pushers podcast. We recorded a three part series where we dive deep into the guts of networking hardware. All three shows are now published on the packet…

  • Is CPU or ASIC responsible for forwarding?

    I received the question below from reader Ned as a comment on my 24-port ASIC post and thought that the discussion was worth a post of it’s own. …Would you be able to speak a bit about the actual physical path or packet flow a packet takes inside the switch itself and how does the hardware…

  • 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…