Does traffic on same VLAN always stay within the domain by default?

[Matt Sebel]

As the subject asks, does inter-VLAN traffic always stay within the domain by default?

In my config, we're allowing all VLANs down the trunks into the Flex-10 Eth modules and then we have vNets configured in Tunneling mode to pass the packets, untouched, to the ESXi servers. We're doing all communication for the ESXi hosts over pairs of 10Gb uplinks and we have the 3 chassis stacked together into a single domain. What I'm trying to understand for certain is whether or not anything communicating on the same VLAN within the domain will always stay within the domain and that it won't actually go out the uplinks to the upstream switches and that this behavior is the default. In this exact scenario, will all the vmotion traffic between the ESXi hosts stay within the back-end domain interlinks?

[Psychonaut · Accepted solution]

The majority of the time it would stay internal, but you can't say it always will.  If the stacking links get congested then the traffic would go out the closest/quickest link to the switch and back down the other side.  

If you want to guarantee that vMotion traffic stays internal create a vNET without uplinks; the traffic will always stay internal.

[Matt Sebel]

Thanks for the clarification. I was pretty sure that was the case, but wanted someone to affirm it for me.

And yes, we'd like to create a vNET just for the vMotion like you suggested, but we may not be able to do that if we want to move stuff between different domains which would require outbound communication to other blades.