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I have a situation in which the ISP can only accommodate a 1GE SFP and single mode fibre, but we have bought 10GE SFP.

Is it possible to get the physical link up when connecting a 1GE SFP to a 10GE SFP?

Assume both sides are multi mode or single mode.

Edit: The testing methods are imperfect, but the results are in. Connecting 10G-850MM-0.1km-MM-SFP+ to eSFP-GE-SX-MM850 fails. Connecting 10G-850MM-0.1km-MM-SFP+ to 10G-850MM-0.1km-MM-SFP+ succeeds.

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    No, you need to get the correct device.
    – Ron Maupin
    Dec 3, 2021 at 17:49

2 Answers 2

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Is it possible to get the physical link up when connecting a 1GE SFP to a 10GE SFP?

Yes - under two conditions:

  1. Both Ethernet variants need to use the same wavelength (e.g. 1310 nm for 1000BASE-LX/10GBASE-LR, or 850 nm for 1000BASE-SX/10GBASE-SR) and medium (SMF or MMF).
  2. The 10G port and SFP(+) module must be compatible with the lower 1G speed - most ports are but very few transceivers ("dual rate") are. Explicit speed configuration for the interface is often required. Some 10G switches don't support dual-rate modules in general and require you to fit a 1G SFP module. Other switches might even link to 1G with a 10G module that isn't flagged for dual rate - mileage varies.
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1GE and 10GE use different frequency and encoding methods. They are not compatible.

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  • Is it possible to put a 10GE SFP in a 1GE interface an negotiate down to 1GE ? Dec 3, 2021 at 17:56
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    It would depend on the SFP, but I've never seen one that does that.
    – Ron Trunk
    Dec 3, 2021 at 18:13
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    @CaineKiewit A 10G SFP+ module doesn't work in a 1G SFP slot in general, unless the switch doesn't care (check) what you plug in at all.
    – Zac67
    Dec 3, 2021 at 20:26

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