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.
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?
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.