Is it possible to use Vlan Tags for Internal only vNets?

[Askar_Kopbayev]

Gents,

we have 2 C7000 enclosures with Flex-10 VC and 460 G6 blades. 10 Blades (5 in each enclosure) run ESXi 4.1. U1. All 4 VCs in both enclosures are stacked in one VC Domain.

we ran several Virtual-Virtual MS 2003 failover clusters. Each of them need heartbeat networks. Currently we use uplinks to our physical core switches to provide these heartbeat networks to all clusters. However, I thought, why didn't we use internal only vNets for such networks? I can edit ESX server profile and use Multiple Networks , but at this point I am a bit confused - in Multiple Network section I have to add vlan ID, this just tells VC what vNet to use for this vlan, but when I go to this vNet without assigned external uplink port I don't see where I can add vlan tag for it. What am I missing here? 

Thanks,

Askar

[Casper42]

Your confusion lies with Uplinks vs Downlinks.

When you create an uplink with multiple networks, you have to use VLAN Tags so the external Switch understands what VLAN the packets go on.
When you use Multiple Networks, you have to use VLAN Tags so the Server understands what VLAN/Network the traffic needs to go on. What most customers do is simply inherit the VLAN Tag of the uplink for the downlink which helps to avoid confusion.

However "Local" Networks that dont have an uplink dont have a VLAN Tag to inherit, and thus you need to provide one so the Downlink side of the house knows how to differentiate Cluster A from Cluster B.

You can basically make up these numbers as long as they are not already in use in your environment. I would suggest having a network admin work with you because an unused VLAN today doesn't mean it will still be unused when that big project lands in your lap next week and the Network guys create some new VLANs.

Also be aware I had heard that some adapters (FlexFab on G7 If I recall correctly) had a bug with VLAN IDs over 999. This was fixed with newer firmware. So if you use a 4 digit VLAN ID and it just plain doesnt work, try borrowing a low VLAN ID and see if that solves the problem. If it does, then you need to upgrade the onboard Flex10/Fab Firmware and re-test with a high VLAN ID.