To Tag or Not to Tag?  vSwitch Tagging Performance - Envision Technology Advisors' blog

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To Tag or Not to Tag?  vSwitch Tagging Performance

About a year ago, I was redesigning a datacenter for one of the largest universities in Massachusetts.

 

During the design process, a member of their team wanted to talk about the performance impact of tagging VLANs at the virtual switch layer (vSwitch or dvSwitch).  They were under the impression that vSwitch tagging came at the cost of a performance hit.  At the time this was news to me, but I could definitely understand the nature of the question and thought it warranted testing.

My sandbox environment consisted of two hosts, tied together with a layer 3 switch.  Each host was the home to a VM that would be used to test round trip latency.

I conducted a total of 6 tests that were a mix of all three virtual adaptor types and both tagged and untagged vSwitches.  The test was to measure packet latency in microseconds round trip from a VM on the first host, through the layer 3 switch, to a VM on the second host, and back.  Below are the raw results offering the minimum, average, and maximum times respectively.

E1000 – vSwitch Tagging

  • Min   0.459
  • Avg   0.491
  • Max  0.581

VMXNET2 – vSwitch Tagging

  • Min   0.457
  • Avg   0.532
  • Max  0.788

VMXNET3 – vSwitch Tagging

  • Min   0.470
  • Avg   0.514
  • Max  0.659

E1000 – vSwitch Default VLAN

  • Min   0.401
  • Avg   0.464
  • Max  0.669

VMXNET2 – vSwitch Default VLAN

  • Min   0.429
  • Avg   0.506
  • Max  0.992

VMXNET3 – vSwitch Default VLAN

  • Min   0.401
  • Avg   0.464
  • Max  0.669

It’s pretty clear that tagging at the vSwitch layer does offer a noticeable performance hit. 

Capture Minimum chart
Capture average chart

This testing is in no way exhaustive, but the preliminary findings speak for themselves.  Bottom line is that I would not recommend tagging at the vSwitch layer unless it’s necessary.

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