I have two redundant core switches I want to connect to a new vSwitch I am setting up on a VMware ESX host. The switch will have two physical NICs each of which will connect to one of the core switches. The core switches are connected.

If this was a physical switch, I would worry about connecting it to both core switches, because this would create a network loop.

Do I need to worry about this for a VMware virtual switch? VMware's documentation says it is not possible to connect two vSwitches in a loop, therefore STP is not required. However, I am worried about connecting two physical switches together via a vSwitch.

  • We're doing the same thing you are trying to do and it works without a hitch. – Scott Keck-Warren Dec 22 '10 at 16:11

vSphere doesn't forward packets like a switch does, so it cannot create a loop (unless a VM on that vSwitch forwards them). I have many vSphere hosts connected to two stacked Cisco switches and it works fine (both with some form of etherchannel and built-in VMWare failover).

  • Do you have spanning tree disabled for the ports, or are you using portfast and bpduguard disable on these ports instead? I have Dell PowerConnect switches, which don't suppport disabling bpdu-guard at the port level (can only do globally). – dunxd Dec 23 '10 at 10:17
  • I have STP portfast enabled on these ports. – Dan Dec 28 '10 at 12:58

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