Our earth is very slowly slowing down, which means every now and then scientists call to add an extra second to our time to compensate. The last was in 2012, the next one is coming up on June 30, 2015 23:59:60 UTC. For more information about this leap second, check timeanddate.com.

Cisco posted an impact analysis on their website with links to bug reports which determine the impact. While most campus products are unaffected, there are some warnings on datacenter products where the leap second update can lead to a crash or lockup.

My intention is not to scare, … Read more


Cisco virtual Port-channels technology is a pretty straight-forward technique: make two switches seem like one switch to a downstream switch, connected with a port-channel. The downstream switch has a single port-channel going upward, which makes the switch high available and eliminating the use of spanning-tree. It looks like this:

vPC in single N7k

Read more about vPC here. For the rest of this post, I’ll assume you know how to configure and use vPC.

In a lab where you have a single Nexus 7000 switch for testing and studying, you would divide it up into VDCs for ultimate usage. OTV, Fabricpath and the … Read more


Cisco OTV (or Overlay Transport Virtualisation) is a technology inside Cisco Nexus switches (7K) for extending VLANs across a routed network. You can read all about OTV here and here. This post consists of an example configuration for a lab where you have a single Nexus 7K and you want to get OTV over multicast running between VDCs and comes from my CCIE study notes for when I was practicing with OTV. I’ve heard some people have issues with getting the multicast configuration working, so I figured I would share mine here.

First off, to create the illusion of … Read more


Cisco has released version 3.1 of its virtualised switch (available for download here). It comes with increased scalability and resiliency, but one very cool thing stood out for me: the Virtual Switch Update Manager or VSUM.

The VSUM is not the only cool improvement on the virtual switch, here’s an overview of changes:

  • Scale
    • Increased Scalability (Advanced Edition) – More than doubles the scale from the previous release. The virtual switch now supports 250 hosts/servers per switch with 10,000 ports per switch. In addition it supports 4094 active VLANs and 16 million VXLAN (6144 active VXLANs) per switch across
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VMware has released a design guide for a network with NSX, Cisco Nexus 7000 and Cisco UCS computing. Perhaps it’s a small glueing attempt from VMware to Cisco, maybe it’s nothing. The thing is, I’m really happy about this design guide, there’ll be a FlexPod for NSX yet! 😉

Read it here: http://www.vmware.com/files/pdf/products/nsx/vmware-nsx-on-cisco-n7kucs-design-guide.pdf

The document outlines a few important tips:

  • Use separate links for the routing between NSX and the Nexus switches. As you don’t want to route over vPC. 
  • Use DVS network shares to prioritise your traffic.
  • Make sure your MTU values are set properly.

It’s a very good … Read more


When you need to only the change the unified ports inside an expansion slot of a Nexus 5500, you do not have to reload the entire switch to activate the unified port changes. You can simply restart only the module like this:

nx5548up-a# config t
nx5548up-a(config)# slot 2
nx5548up-a(config-slot)# port 1-16 type fc
nx5548up-a(config-slot)# end
nx5548up-a# copy run start
nx5548up-a# poweroff module 2
nx5548up-a# no poweroff module 2

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