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Internal chassis blade communications with Virtual Connect

Trusted Contributor

Internal chassis blade communications with Virtual Connect

Stephen was looking for help on Virtual Connect for a customer situation:




> Hi - customer wants to create two separate SUSes on the FlexFabric

> modules in rear bays 1 and 2 so that they operate in active/active

> mode to give the full uplink bandwidth.


> If they do this they have asked the following 3 questions:-


> (1) If blades within the chassis need to communicate via the SAME port

> (e.g. port 1 or port 2) does traffic go out to the upstream switches

> or do the VC modules route traffic for the same chassis directly back

> down the relevant downlink? (I'm pretty confident that the answer is

> YES but I need confirmation).


> (2) if two blades within the chassis need to communicate via DIFFERENT

> NIC ports (e.g. Blade-X via sends traffic via port 1 to port-2 on

> Blade-Y in the same chassis) will this traffic be routed/bridged

> across the X7,X8 cross-links OR will it need to travel out of the VC

> uplinks to the external switches and then be sent back to BladeY. So

> they will have created, say, VLAN101-1 on SUS1 and VLAN101-2 on SUS2

> and ideally would prefer these two networks to communicate across the

> cross-links rather than be routed via the external switches. I suspect

> the answer to this is NO because there is no communication between

> different VLANs across the interconnect? Can anyone confirm or deny?


> (3) Today they use Cisco blade switches. For VMWare ESX, they tell me

> all network traffic from any individual VM can only be routed out

> through one port on the host blade (I guess because they cannot create

> an active-active trunk across two Cisco blade switches (unless they

> use the Cisco VBS feature which they don't, as it has other issues).

> They can manually load balance different VMs across the two blade

> ports but would prefer to create a single aggregated link from the two

> 10G ports on the BL460cG7 and give every VM access to the full 20G

> uplink bandwidth (or some Flex-10 fraction of that). I know that

> aggregation of the two NICs on the BL460cG7 can only be done by the

> operating system in the case of Windows and I assume that ESX 4.x can

> do the same but I need confirmation. Does ESX 4.x allow creation of a

> single aggregated 20G NIC on the BL460cG7? Again I think answer is YES

> but I need confirmation.




Andreas replied:






Here some rules how traffic is forwarded with VC:


- If traffic stays in the same SUS it will switched locally and use the cross links (in a 2 interconnect module design)

- Traffic between 2 different SUS need always be switched by the next uplink switch

- Load Balancing on ESX can have different flavors with VC 

         Route based on the originating vSwitch port ID <- recommended for most setups

         Route based on source MAC hash

         Route based on IP hash   

VC does not support LACP on downlinks


VC does never route. It just forwards a packet. Just to avoid the wrong terms.


Hope this helps already.




Other comments or suggestions for Stephen?