I'm trying to connect a Cisco Catalyst 3750 12-port SFP switch to a RuggedCom RSG2100 with fiber ports. The Cisco has a third-party SFP (GLC-LH-SM) that shows in "show interface" as 1000Base-LX, and the CLI gives me no options to set the speed and duplex of this port. The RuggedCom switch shows the port to be 100Base-FX. The Cisco is down/down when connected, and the RuggedCom blinks repeatedly until fast link detection fails, the whole time reporting that the port is down.

Will I need some 100Base-FX Cisco SFP for these to talk? I've tried trunking both ports to no avail. Thanks.

1 Answer 1


1000base-LX and 100base-FX are very different beasts. The GLC-LH-SM will not operate at 100Mbps. Surprisingly, Cisco does make a GLC-FE-100FX and GLC-GE-100FX.

(Consult the interop guide for which one you need.)

  • Thanks, I will be looking at the GLC-GE-100FX as a replacement SFP then.
    – armani
    Commented Jun 4, 2014 at 19:58

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