About connecting CX2 to CX3

Hello all, I am new to here, and I googled very long time and I still cannot find a detailed info about connecting QDR to FDR.

As I know infiniband is auto-negotiate (switch to HCA and QDR to DDR or SDR), but can I connect FDR to QDR HCA to HCA?

Thanks for any input.


The first question I ask is where is your Subnet Manager running. Even back to back connections need a subnet manager. If you are running Linux on both hosts - go to one host and run

$/etc/init.d/opensmd start (As root obviously)

If that doesn’t bring up your link the next thing to look at is OFED drivers and things like that.


IB supports Back to Back fabrics. You will need to run a Subnet Manager on each back to back link.

No ramifications - with a back to back, multicast and unicast is almost the same thing. - there is no need to configure switch tables.


I dont know if they can communicate each other with difference bit rate QDR <>FDR

I have SM on both machine.

And I can bring up both ports, but I afraid the card will smoke if they are not supported

I do not have an answer to this question but a comment.

Whether IB supports fabrics that are made up of point to point connections is a popular question I believe. It is not clearly documented.

Are point to point links supported (sounds like the answer is yes)?

Are there any ramifications to operating behavior if a switch is missing? For instance will multicast work if the SA has no switch tables to configure?