While I am no CCNA certified, I've been messing around and configuring Cisco switches for the past 6-7 years so I know my way around. I've been having an issue for the past few weeks that I can't figure out and I hope I can get some replies here that will help me out.
We recently moved our main distribution switch (previously a Cisco 4510R) to a new distribution switch (stack of 4x 3850'). The duplex issue began after the migration. Some of the trunks to some buildings are negociating at half duplex since we switched over the new stack. Previously, these buildings were connected in the 4510R with fixed MT-RJ connectors running at 100Mbps. At the building's end, some buildings are connected with Wireweks tranceivers to Cisco 2960 swiches while other buildings are connected to GLC-GE-100FX into Cisco 2960 X. For the migration to the stack of 3850', we bought some Cisco GLC-GE-100FX to replace the fixed MT-RJ connectors and thought it would work. It doesn't. The buildings are negociating at half-duplex with the GLC-GE-100FX. This happens either if there's a tranceiver at the building's end or an SFP. There is no duplex half in the config of the trunk, all is negociated auto. Forcing duplex full results in no connection.
We are now thinking about the fibers being an issue. We tried switching to other pairs, but still running with the same issue. Those fibers are Multi-Mode and probably 15+ years. Could it be the fiber quality ? Could it be that the MT-RJ connectors in the previous 4510R were more "powerful" than the new SFPs ?
Thanks for any comments.