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SFP GLC-SX-MM module speed issues

Hi, I'm having difficulties in connecting such SFP module to a PTT device - at&t canoga perkins 9145 - at 100Mbps speed. Found documentation that such fiber module does not support 100Mbps but only 1000Mbps... not sure however if there's a config mistake, as follows:

Interface GigabitEthernet0/0

description ---

bandwidth 100000

no ip address

duplex auto

speed 1000

media-type sfp

negotiation auto

Any clue is appreciated. Thanks.


Re: SFP GLC-SX-MM module speed issues

You are correct, an optical SFP will not negotiate its speed parameter. Their speed is fixed.  

You didn't mention which Cisco switch you were operating.  If your  switch is compatible (compatibility document link below) with SFP part number GLC-GE-100FX,  then this SFP module will allow you to operate a 100Mbps link when installed in your switches GE SFP slot.

100M SFP Compatibility Matrix


If you ever need GE over this link, you will have to swap the SFP  module with a GE SFP module.

Hope this helps!


Community Member

Re: SFP GLC-SX-MM module speed issues

Thanks Tom. Actually I've a CS3845 router. As per the compatibility info link you've shared with me, this 100FX module isn't compatible. I'm afraid that with this setup - telco device with a MM fiber connection at 100Mbps trying to establish with my 3845 optical SFP - I wont be able to achieve unless I change it to a SFP copper on both sides, change the 'media-type' interface parameter and then adjust the speed. Does it make sense or do you have any other tip ?

Thanks again !

Re: SFP GLC-SX-MM module speed issues

If I understand your situation, the distance between your 3845 and the telco device is short enough to use UTP?  If so, then connecting the two devices using FE over copper would seem most practical and sound. 

If you need to use fiber for the reach, then you could use media converters to convert from copper to fiber.  You would still have to change the 3845 SFP to copper (config'd for FE). The downside to this is its another piece of hardware that can fail.

3845/Copper SFP FE ---->  FE Copper/Media Converter/FE Fiber ----------> FE fiber/Telco device

Media Converter Example



Community Member

Re: SFP GLC-SX-MM module speed issues

Thanks Tom. Yes, distance is not an issue. I'll try changing to FE copper then and see what the result is gonna be. I'll post it as soon as I get it.

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