Upgrading the virtual network to use NSX is not a heavy or large task. It can be, depending on what you are doing, but the basics are fairly straightforward. These basics are not the wholesale replacement of your existing virtual network. They are not the inclusion of new forms or routing in your virtual environment. The are the addition of NSX on top of what you already have. Once you have NSX in place, then you can dream, plan, and adopt those better ways of managing and creating virtual networks. Continue reading vSphere Upgrade Saga: NSX in 8 Easy Steps
This was a painful upgrade, but I had lots of help from various sources. The main element is to ensure you follow the vSphere Update Sequence. Update everything in that specific order: do not differentiate. This is important, as some things will not upgrade if they are out of order. This part of my vSphere Upgrade Saga upgrade was far from smooth.
vCNS 5.1 replaces vShield 5.1, and if you do not add new nodes during your installation, you can easily perform all upgrades without removing any components of vShield. vCNS upgrades will upgrade all components of vShield.