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Two ESX servers in the same enclosure...

Trusted Contributor

Two ESX servers in the same enclosure...

Gary had a customer question on ESX and Virtual Connect:




Customer has two ESX servers in the same C7000 enclosure.  The VC is set for tunneling mode.  ESX servers both have a port group with the correct VLan ID set for VMs to use. Private network is not checked in the VC network config.


The question is, can a VM on one server talk to a VM on the other server?  Will the traffic stay within the VC or since it is tagged will it need to leave the VC?




Carl and Chris joined the conversation:




Carl said: 

If the networks are tunneled, the traffic will always be switched upstream. The question of whether the VMs can talk is a matter of security/policy on the upstream switch.


The VC won’t switch traffic between VMs if their VLANs are being tunneled through.


Chris reaponded: 

“If the networks are tunneled, the traffic will always be switched upstream.”


Sorry, but this is simply not true Carl.  VC does look at the source and destination MAC addresses (L2 forwarding), but not the VLAN ID when the Ethernet Network is set as a Tunnel.  What VC does is 802.1Q-in-Q.  Meaning, the “customer VLAN ID” is moved into the payload of the frame, and VC adds its own VLAN ID (called the Provider VLAN ID.)  This turns the entire Ethernet Network into a single broadcast domain, no matter how many VLANs the customer is tunneling.  VC removes the Provider VLAN ID, and moves the Customer VLAN ID back to the 802.1Q section of the frame.


So, to Gary’s question, if the ESX hosts had the exact same networking configuration, and you had designed an Active/Standby configuration, then each VM would communicate with each other by VC forwarding their respective frames to each ESX servers NIC port.




Other comments? Are you communicating between ESX servers within a chassis and not going up to the switch? Let us know.