NIC Teaming & Switching Loops?

[euroscriptde]

Hey folks,

when reading documentation i wondered about the switching loop issue on p/vswitches - lets assume:

• we got 5 VMs with each having 1 vNic which are interconnected to the same vSwitch.

• this vSwitch has connection to 2 pNics connecting to a (HP) pSwitch, with configuration route based on the originating port ID.

According to my logic (in a physical world) a connection between 2 switches creates loops, at least when one device is broadcasting, in the physical world, STP adresses this issue.

As i could not find any hint about looping frames in a vSwitch <-> pSwitch environment, could any1 explain

• why a vNic broadcast frame does not loop around the vSwitch / pSwitch?

• if it indeed does, how to adress this issue in the virtual/physical-combined world;)

Regards,

Philipp

[AndreTheGiant]

You cannot have loop.

Usally each "virtual port" on the vSwitch has only one uplink.

Team is simply done, splitting some "virtual port" on different uplink.

The only execption is when you use "Route based on IP hash" team policy. But in this case you have to configure your ports on physical switch with 802.3ad link aggregation.

Andre

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[MKguy]

There is no issue with loops, since a vSwitch connected with multiple physical uplink NICs doesn't bridge these uplink connections to each other like a normal physical switch. A (broadcast) frame will never travel through one uplink pNIC and then be sent out through the other uplink pNICs, instead it will only be forwarded to the VMs of that port group. The uplink connections are solely for the purpose bridging the VMs traffic to the outside. You can only create loops if you set up VMs with multiple vNICs connected to multiple uplinks and configure the guest OS to bridge these connections.

Check out these great whitepapers on how ESX networking works, including comparisons between ESX vSwitchs and ordinary physical switches.

http://www.vmware.com/files/pdf/vmi_cisco_network_environment.pdf

http://www.cisco.com/web/BE/learn_events/pdfs/Server_Virtualization.pdf

VMware infrastructure enforces a single-tier networking topology within the ESX Server. In other

words, there is no way to interconnect multiple virtual switches; thus, the ESX network cannot be

configured to introduce loops. Because of this, the vSwitch on the ESX host does not execute the

Spanning Tree Protocol (STP).