Data flow between VMs

[Amit Vyas]

Hello,

I have a question that how data flows between two VMs.

For example my TestVM-1 reside on Blade-1 of Chassis-1 and TestVM-2 resides on Blade-2 of Chassis-2

In above scenario how my data will flow in shown / attached diagram.

• Data will flow from FI to FI?
• Data will from Up-stream switch in my case 5548 switch?

Regards,

Amit Vyas

[Robert Burns]

It depends which fabric your VM gets pinned to.

If your two VMs need to communicate, their path is dependent on their fabric pinning.  If both VMs reside in the same Layer 2 domain (VLAN) and are pinned to an adapter uplink which go to the same fabric interconnect (both to A or both to B), then the traffic goes up to that FI, and back down to the destination VM on the other chassis.

If the two VMs are in the same Layer 2 domain, but pinned to opposite fabrics, then the traffic will go northbound of UCS (to your N5Ks in this example) and back down to the other Fabir Interconnect, and down to the destination VM.

If the two VMs are in different Layer 2 domains (different subnets) then traffic will go northbound to a router/gateway, and come back down to the FI where the destination VM's MAC address was learned.

Keep in mind there is no data traffic directly between FI's.  If traffic from one FI needs to reach the other, it needs to go Northbound and back down.

Regards,

Robert

[Amit Vyas]

Thanks Robert for your quick revert

VMs reside in same VLAN.

I am sorry to say but I didn't understand the fabric pinning part which you have mentioned in your reply.

What I understand is suppose my vNIC-0 which prepfered path is Fabirc-A for Blade-1/Chassis-1 server and for vNIC-0 on Blade-2/Chassis prefered path is Fabric-A then traffic will flow via FI only and will not go to my 5k

For another thing.. if my vNIC-0 prefered path is Fabric-A on Blade-1/Chassis-1 server and for vNIC-0 on Blade-2/Chassis prefered path is Fabric-B then traffic will flow like vNIC-0 -> FI-A -> 5k-A -> 5k-B -> FI-B -> vNIC-0 or it will flow like

vNIC-0 -> FI-A -> 5k-A -> FI-B -> vNIC-0

Do let me know if my understanding is correct in both

Regards,

Amit

[Robert Burns]

Comments inline.

Robert

VMs reside in same VLAN. 
I am sorry to say but I didn't understand the fabric pinning part which you have mentioned in your reply. 
[Robert] When I say "pinning" I'm referring to which uplink is chosen to carry the VMs traffic.  We use the term pinning because the traffic from any single source is "pinned" to one uplink in the manner vs being shared across multiple. 
What I understand is suppose my vNIC-0 which prepfered path is Fabirc-A for Blade-1/Chassis-1 server and for vNIC-0 on Blade-2/Chassis prefered path is Fabric-A then traffic will flow via FI only and will not go to my 5k
[Robert] Correct.
For another thing.. if my vNIC-0 prefered path is Fabric-A on Blade-1/Chassis-1 server and for vNIC-0 on Blade-2/Chassis prefered path is Fabric-B then traffic will flow like vNIC-0 -> FI-A -> 5k-A -> 5k-B -> FI-B -> vNIC-0 or it will flow like 
vNIC-0 -> FI-A -> 5k-A -> FI-B -> vNIC-0
[Robert] vNIC-0 -> FI-A -> 5k-A -> FI-B -> vNIC-0
Do let me know if my understanding is correct in both
Regards,
Amit

[Keny Perez]

Amit,

You got your answer already from a great source.

I bet this videos (7a & 7b) will also help you understand better the concept of pinning and how we move traffic at the Fabric Interconnect level: 

http://bradhedlund.com/2011/03/08/cisco-ucs-networking-videos-in-hd-updated-improved/

Some stuff might have changed f you watch other videos, they were posted a while already but the idea is the same and if you have more doubts, feel free to post your questions in the community.

-Kenny