Nexus 1000v UCS Manager M81KR

Question

Hello everyone
I am confused about how works the integration between N1K and UCS Manager:
First question:
If two VMs on different ESXi and different VEM but in the same VLAN,would like to talk each other, the data flow between them is managed from the upstream switch( in this case UCS Fabric Inteconnect), isn'it?
I created a Ethernet uplink port-profile on N1K in switch port mode access(100), I created a vEthernet port-profile for the VM in switchport mode access(100) as well. In the Fabric Interconnect I created a vNIC profile for the physical NICs of ESXi(where there are the VMs). Also I created the vlan 100(the same in N1K)
Second question: With the configuration above, if I include in the vNIC profile the vlan 100 (not as native vlan) only, the two VMs can not ping each other. Instead if I include in the vNIC profile only the defaul vlan(I think it is the vlan 1) as native vlan evereything works fine. WHY????
Third question: How it works the tagging vlan on Fabric interconnectr and also in N1K.
I tried to read differnt documents, but I did not understand.
Thanks                 

Answer 1

Since you have defined switchport mode access vlan 100 on uplink port-profile of Nexus 1000v, it sends all ethernet frames untagged(without 802.1q tag).
When you include in the vNIC profile the vlan 100 (not as native vlan) ONLY like below screenshot, untagged frames are dropped because UCS expects all frames received on this port as tagged frames.
When you change vNIC template to include default vlan as native vlan ONLY like below screen shot, you basically bridge two vlans (vlan 100 and vlan 1) because UCS FI now puts all untagged frames in vlan 1. and sends untagged frames to other ESXi host and ESXi host again bridge vlan 1 to vlan 100 with switchport mode access vlan 100 on uplink port profile.