I created several virtual machines in my VMware ESXi 5.1 host whose OS was Ubuntu 12.04 LTS. The installation was smooth and fast, but after they booted up for the first time there was no available network connections on any of the VMs. I even tried installing Ubuntu 12.10 but the exact same problem occurred on this OS as well.
After playing around with the VM hardware settings, I figured out what the cause was. The problem had to do with the default network adapter options. You must choose the VMXNET 2 (Enhanced) adapter type for Ubuntu virtual machines in order to get it working.
If you find yourself with the same issue, just add in a new network adapter and choose the correct adapter type. An example screenshot is below.
This may have been discussed in other blogs, but I couldn’t find any. I hope this helps someone out.