Today we have a very painful and time-killing problem. Be careful NOT to run into the same issue.
We using X440-G2 with 10GB GBICs on the Uplink ports (51-52 - with Dual 10GB LIC) linked to 2x X670-G2 also with 10GB GBICs.
Some of my collegues configured the X440-G2 BUT do NOT install the 10GB License.
If you connect that Switch to the CORE you does not get a link. But light comes out of the fibre cable and seemed to be OK. If you check transceiver information on CORE switch you can see that you have excellent signal - but the link on the CORE Switch does not come up! Damn!
If you have a look at the X440-G2 the log tells you that the 10GB Port have a 10GB GBIC but you do NOT have a 10GB license, so the speed is reduced to 1GB!
Does this make sense ?
The result is that the 10GBIC sending out a signal but a 10GB GBIC cannot never run in 1GB mode. So there will never ever be a link. Talking with some other network guys telling me that a very usual mistake a lot of people running into this pitfall.
From my point of view it was better if the developers disable the 10GB GBIC completely to avoid such tricky problems!