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I need to install new SFP's in a location; however, I need them to connect to existing switches and I'm not sure what SFP type they are. All I know is I've got MM Fiber.

If I installed Cisco GLC-SX-MM 1000Base SFP's, would that cause an issue if the other end of that fiber was connected to a 100Base SFP, or do I need to have matching speeds on both ends?

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3 Answers 3

If I installed Cisco GLC-SX-MM 1000Base SFP's, would that cause an issue if the other end of that fiber was connected to a 100Base SFP? Or do I need to have matching speeds on both ends?

Your speeds must match

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Thanks Mike. Straight and to the point. –  Ryan Jul 18 '12 at 14:12
    
Ryan, theoretically you can have autonegotiation on fiber media. Practically speaking, I have not seen a vendor do this recently. Pluggable optics (GBICs / SFPs) make it too easy to swap the Tx speed without integrating PHY/optics autoneg support (which would require additional vendor test efforts). Copper media routinely supports autonegotiation –  Mike Pennington Jul 18 '12 at 17:22
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There are some handy links in this other serverfault question which might help.

How compatible are sfp's really?

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It depends on what you mean by cause an issue. It won't break anything but you won't get a link either. They must be the same. SFPs are hot-swappable so you can remove it to inspect the label without damaging it. Additionally, you can do a show interface status to have the switch tell you the model SFP that is installed in a port.

Not only can you not mix speeds but you should stay away from mixing sfp models as well.

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Thanks for the response Mike and Paul. What I meant by an issue was "will it not work". So I'll need to find out the speed / model next time I'm at site. I appreciate the help. –  Ryan Jul 18 '12 at 14:11
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