The C3120X blade switch currently doesn't support the X2-10GE-LR (long-range, single mode fiber) module according to this documentation: http://www.cisco.com/en/US/docs/interfaces_modules/transceiver_modules/compatibility/matrix/OL_6974.html
1) Is future support planned (via software) or is it a hardware, asic reason why this interface isn't supported ?
2) What alternatives do i have to connect
these switches with single-mode fiber ?
I did some digging and it appears the LR optic will be supported in the 3120X blade switches this March with the 12.2(50)SE software release. Hopefully this comes as good news.