SFP's go to down/down when put on a fiber backbone

[jimmycher]

I have two switches, both with SFPs.  When I connect them directly, with a fiber patch cable, they work fine and trunk well.  When I put them over a fiber backbone, they both go to down/down.  We flashlight tested three separate backbone connections, and swapped out the patch cords.  Nothing works.  Completely out of ideas.  Need help quickly.  Thanks.  JC

[cmarva · Accepted solution]

just with the info you've provided it sounds to me like you need to flip the polarity (xmt and rcv) on one of the fiber jumpers

[jimmycher]

thanks
crossing the backbone fixed it.