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Virtual Connect Private Networks

Occasional Advisor

Virtual Connect Private Networks

Could someone please explain how Virtual Connect "Private Network" functions. If two hosts in a Virtual Connect domain are connected to the same VC network and are in the same IP subnet, how can they communicate with each other if the VC network is set to "Private".

I have seen some comments in this forum suggesting that the traffic would flow up the uplink to an external switch and then come back down the same uplink to the destination server blade. But, I doubt that many switches would forward a packet back down the link on which it was received, especially if the destination MAC address was not yet in the switch's MAC address table.

The Virtual Connect User Guide states that "Servers on the network can only communicate with each other through an external Layer 3 router that redirects the traffic back to the VC domain." But that would imply that a server host would send a packet to its ip gateway even though the destination server was on the same subnet, as opposed to sending an ARP to find the MAC address of the destination.

Thanks for any clarification.
Honored Contributor

Re: Virtual Connect Private Networks

Hi Paul,

The way I understood this from HP support is consistent with what you found on other posts.

For example the servers in bays 1 and 2 belong to the same virtual network. If the server in bay 1 pings the server in bay 2 that traffic will never leave the enclosure... unless "private network" is enabled for that virtual network.

As for routing traffic back down the same port, that is something a layer 3 device has no problem with... but I agree that a switch (usually layer 2) would be confused. I think for that reason the traffic within a private network would be headed further upstream if the enclosure was connected to a switch.

Check page 30 of this document for a clearer explanation:

good luck!
Neighborhood Moderator

Re: Virtual Connect Private Networks

So, there is some confusion on this topic.

1. A VC Ethernet Network marked as Private simply states no assigned NIC will be able to communicate with other systems whos NIC is also connected to the same VC Ethernet Network. For instance, if HOSTA has one a single NIC defined in its Server Profile, and that NIC is assigned to VNET1 (which is marked as a Private Network), and HOSTB is configured exactly the same way, HOSTA and HOSTB will never talk to each other while they are in the same VC domain. HOSTA and HOSTB will be able to communicate with other systems on the network OUTSIDE of the VC domain (i.e. a backup server.) This is very similar to the Isolated PVLAN feature within Cisco switches. It is NOT the same thing.

2. A VC Ethernet Network marked as Private will never have the traffic egress the uplink port to the upstream switch, and then ingress back the same path. This is a vioaltion of 802.1D rules, specifically referring to "Hair-pinning."

3. If HOSTA's NIC1 is assigned to say VNET1 (marked as a Private Network) and HOSTB's NIC1 is assigned to VNET2 (also marked as a Private Network), their communication would be handled via the L3 gateway connecting their subnets; unless there is an ACL between the path that prohibits that communication.)

Re: Virtual Connect Private Networks

Hallo Mr. Lynch,
can post a link to an HP document there I can read this details about Virtual Connect "Private Network" and the vioaltion of 802.1D rules ?