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 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, impede access to other rack units or blades.

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Getting started with Network Packet Generators

bit blaster

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 to test throughput, latency or loss, a stateless packet generator will do the trick. The test hardware will use an ASIC to produce line-rate 10G traffic or higher. The Cisco Enterprise Testing Book calls this a ‘bit-blaster’ which I love. In the wrong hands it can also be a ‘network-melter’.  Continue reading

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 still some debate about whether 2Gbps of throughput is sufficient for a single-radio Wave2 AP.

Some companies may not be willing to invest the time and expense to swap out their copper for fiber or run yet more copper to their APs. The NBase-T standard 802.3bz provides an alternative approach, promising speeds of 2.5Gbps or 5Gbps over Cat5e cabling over 100 Meter runs.

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East West Segmentation With ACI


dome-664000_640East/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. Continue reading

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 a previous post, but I wanted expand on this and add a quick graph to back up the argument.

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