I wrote an article a while back regarding VLAN configuration when running vSphere ESXi on top of Cisco UCS.
A comment pointed out that all vNICs are automatically configured as trunks. I had not heard of this before, so I got into the CLI to take a look.
Here’s a VLAN configuration screen in the UCSM GUI for a sample vNIC:
Check out the running configuration for this vNIC on the underlying NX-OS CLI.
UCS-FI-A(nxos)# show run int veth782 interface Vethernet782 description server 1/7, VNIC BARE-IPST-PROD-A switchport mode trunk untagged cos 2 no pinning server sticky pinning server pinning-failure link-down no cdp enable switchport trunk allowed vlan 370 bind interface port-channel1290 channel 782 service-policy type queuing input org-root/org-root/ep-qos-Silver no shutdown
As you can see, even though we have a single VLAN checked in the GUI, the vNIC is still a VLAN trunk, and simply prunes all other VLANs off of the trunk.
This also means…
UCS-FI-A(nxos)# show int veth782 sw Name: Vethernet782 Switchport: Enabled Switchport Monitor: Not enabled Operational Mode: trunk Access Mode VLAN: 1 (default) Trunking Native Mode VLAN: 1 (default) Trunking VLANs Enabled: 370 Administrative private-vlan primary host-association: none Administrative private-vlan secondary host-association: none Administrative private-vlan primary mapping: none Administrative private-vlan secondary mapping: none Administrative private-vlan trunk native VLAN: none Administrative private-vlan trunk encapsulation: dot1q Administrative private-vlan trunk normal VLANs: none Administrative private-vlan trunk private VLANs: none Operational private-vlan: none Unknown unicast blocked: disabled Unknown multicast blocked: disabled
the native VLAN for this vNIC is still 1, UNLESS you select one of the radio buttons.
You know….in case you haven’t learned to double-check the underlying configuration when in doubt. Took me a while to learn that lesson.