10Gig connectivity for IDF closets giving low power warnings

[Eric Lindsey]

We are starting to connect our IDF closets with 10Gig connections to our core 6509s.  We have two 6509s running in VSS mode.  Our IDF closets connection to both 6509s today with 1 Gb uplinks.  One connection is a single mode connection and on connection is a multimode connection.  We are trying to move these connections over to 10gig connections.  The Single mode connection is not a problem.  We are using a LR module with single mode cables and it works perfectly.  The multimode connection is the one giving us issues.  The multimode path between devices is only about 80 meters.  We are trying to use LRM modules for the uplinks.  We have tried using mode conditioning multimode cables to make the connections but the link will not come up.  The link will come up with normal 62.5 multimode cables but the switch is complaining about   Low RX power warnings of -9.5 dBm.  Is there any combination that will work to bring up the multimode pathway with 10Gig without any power issues?          We are hoping that we will not need to replace our fiber to our idf closets.      

[jstevens13 · Accepted solution]

My first thought is that you should check your fibers.  80 meters of of multimode should have very little attenuation normarally, unless there are issues with bad splices or dirty connectors.  Every patch point should be cleaned with a fiber cleaning kit and inspected. 

The other thing to note here is that all of the 1Gb SFPs of that you may have been previously using on this link had a minimum receive threshold of down to at least -19 dBm (see table 2 on this page) whereas the 10Gb SFP+ module that you are now using has a minimum receive threshold of only around -8.4 (see table 2 on this pdf).  My point being, that this fiber link may have had an issue for a long time, but the older optics were just dealing with it better.