We are trying to bring out a series of 10G links between our Nexus 7k core and 7606 edge routers. We are using 10GBase-SR for intra-building connections (SFP+ in Nexus and X2 optics in the 7606 routers); however, none of the links will come up. If we connect the SFP+ SR optics back to back in Nexus the 10G links come up. The X2 optics are located in 6708 line cards in two separate 7606 routers (other 10G links are working in the 7606). The fibre pairs have been swapped around to avoid any obvious TX/RX transpositions. I am not aware of any interoperability issues between X2/SFP+ 10G optics? The Nexus is running 5.0(2a) and the 7606s are running 12.2(33)SRD4.