SFP and SFP+ Compatibility Issues

Recently, people have gotten the question about whether I can use the SFP transceivers in a 10g SFP slot. Users who purchase a 10G switch wondered if they could use SFP modules in the SFP+ slot (since they both have the same size and use the LC connectors) to achieve 1G data rate. Or can I use the SFP+ modules in SFP slot to have the 10G data links? To deal with this doubt, researches have been made to provide the objective solutions here.

In Most Cases, SFP Can be Plugged into SFP+ Ports

If you are asking whether an SFP+ port will accept an SFP, then the answer is almost certainly yes. Not all SFP transceivers will be compatible with all devices though. Some device makers require that the SFP or SFP+ transceiver have a branded firmware on it. That is why some SFPs are marketed as Cisco brand or HP brand or Dell brand or whatever. The hardware is all from the same Chinese factory but before they are shipped they are loaded with a firmware that marks them as being compatible with a particular brand of device. You don't need the same brand of transceiver at both ends unless you use the same brand of switch on both ends. The transceiver should be purchased to be compatible with the device you are inserting it into (not connecting the cable to). This isn't always necessary, only some devices have strict compatibility requirements. However, you really never know until it is too late so make sure you buy your SFPs from somewhere that will assure the compatibility and has a good return policy.

The most I have had to do to make an SFP work in an SFP+ slot is to configure the interface before inserting the SFP. Sometimes you have to tell the switch/router vendors that the port is going to run at 1000 megabit before you insert the SFP.

SFP+ Can’t Auto-negotiate to Support SFP Module

Most SFP+ ports accept SFP optics, but it can’t auto negotiation to the 1G SFP modules. In fact, most (95+%) SFPs and SFP+s will only run at the rated speed, no more, no less. Besides, there is no such thing as a SFP+ that does 1G on one side (towards the fiber) and then does 10G on another side (towards the unit). Though we can use SFP in SFP+ ports in many cases, that doesn’t mean a SFP+ plugged into the SFP port can support 1G. For example, a Cisco Meraki SFP-10GB-SR can only support 10G data rate plugging into a SFP+ slots in the 10G switch.

Additionally, in a fiber link, if we plug a SFP in the SFP+ port on one side (1G), and then plug a SFP+ in the SFP+ port on the another side (10G), this may not work! You just can’t have 10 GbE at one end and 1 GbE at the other. For this question, if you use SFP+ copper twinax cable, it also can’t negotiate down to 1G.

Conclusion

To sum up, the SFP+ slots will take 1Gb SFP optics though, SFP modules can not be connected with SFP+ optics. And make sure you use the same fiber link at the both ends in a fiber optic network. This is actually a complex question, there is no exact answer now. Always remember to talk with your vendors first before making the next move, or you will end up with an error. FS.COM as a professional telecom supplier, offers a full range of optical devices including fiber optic cables, optical transceivers (SFP/SFP+/QSFP+/CFP, etc.), fiber patch panels, DAC/AOC cables.