I have two vSwitches like this:
On vSwitch0, I have 3 VMs.
On vSwitch1, I have 1 VM.
I want to know if it is possible for the VM on vSwitch1 to communicate with a VM on vSwitch0 without going through the physical NIC (or vNIC), since it's on the same host. For instance, if I unplug the vmnic1, can LABUNIX01 still communicate with a VM on vSwitch0 since it's on the same physical host ?
No they cannot. Virtual machines on two different vSwitches can't communicate with each other, except through the physical network or through a virtual machine acting as a "bridge" between the vSwitches (one vNIC connected to each of the vSwitches).
Nope. They're separate and discrete vSwitches for a reason. Why are they separate in this case? If they need to remain separate, you could bridge them through an external switch or potentially add another vNIC from the relevant VM's and join them into a third vSwitch.
You can have all the VMs on the same vSwitch and use multiple uplinks to the physical switch for redundancy.
Assuming that there's a good reason for the current vSwitch separation, another option is to add a third vSwitch, with no uplink ports, then add virtual adapters to both VMs and assign them to the new vSwitch. You'll need to configure IP addressing, etc, but you'll have network connectivity without requiring access to to the physical network.
However, I believe this configuration (VM connected to a vSwitch with no uplink) will break vMotion, and VMs on the new vSwitch will not be eligible for vMotion.
Both joeqwerty's and ewwhite's answers are correct, for a solution you can set both nics to the same switch and add all the VMs, use different VLANs to segregate the networks.
