Posts Tagged ‘gre’


The recording of last week’s seminar on Introduction to DMVPN for CCIE R&S v5 Candidates is now available to view here.  This is the first of many new free seminars on new topics that have been added to the CCIE R&S version 5 blueprint.  New upcoming sessions will include IPv6 First Hop Security, IPsec LAN-to-LAN tunnels, GET VPN, IGP Convergence & Scalability, and BGP Convergence & Scalability, just to name a few. Feel free to submit requests for additional topics in the comments below.


Good luck in your studies!

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Edit: For those of you that want to take a look first-hand at these packets, the Wireshark PCAP files referenced in this post can be found here

One of the hottest topics in networking today is Data Center Virtualized Workload Mobility (VWM). For those of you that have been hiding under a rock for the past few years, workload mobility basically means the ability to dynamically and seamlessly reassign hardware resources to virtualized machines, often between physically disparate locations, while keeping this transparent to the end users. This is often accomplished through VMware vMotion, which allows for live migration of virtual machines between sites, or as similarly implemented in Microsoft’s Hyper-V and Citrix’s Xen hypervisors.

One of the typical requirements of workload mobility is that the hardware resources used must be on the same layer 2 network segment. E.g. the VMware Host machines must be in the same IP subnet and VLAN in order to allow for live migration their VMs. The big design challenge then becomes, how do we allow for live migrations of VMs between Data Centers that are not in the same layer 2 network? One solution to this problem that Cisco has devised is a relatively new technology called Overlay Transport Virtualization (OTV).

As a side result of preparing for INE’s upcoming CCIE Data Center Nexus Bootcamp I’ve had the privilege (or punishment depending on how you look at it ;) ) of delving deep into the OTV implementation on Nexus 7000. My goal was to find out exactly what was going on behind the scenes with OTV. The problem I ran into though was that none of the external Cisco documentation, design guides, white papers, Cisco Live presentations, etc. really contained any of this information. The only thing that is out there on OTV is mainly marketing info, i.e. buzzword bingo, or very basic config snippets on how to implement OTV. In this blog post I’m going to discuss the details of my findings about how OTV actually works, with the most astonishing of these results being that OTV is in fact, a fancy GRE tunnel.

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