Using a 2.5GBASE-T SFP or SFP+ module in DEC750 [solved]

[JanW]

Hi all, I recently acquired a DEC750 appliance and would like to connect it to a home fiber box which has a 2.5GBASE-T port (no 10G, sadly). Does anyone know if there is a way to connect the DEC750 to that box at 2.5G speeds, for example using the SFP 2.5GBASE-T module from FS (https://www.fs.com/fr/products/139650.html) or a mutli-speed RJ45 SFP+ module such as the Mikrotik S+RJ10 (rev.2) (https://mikrotik.com/product/s_rj10 )?

I understand that the DEC750 must be able to support 2.5G speeds internally, and I don't know if that's the case? And then it would be a question of SFP/SFP+ module compatibility and drivers.

Any insights or pointers where to look for the relevant info would be greatly appreciated! A quick search in the forums didn't seem to turn up any results.

Thanks!

(edit: fixed botched URL)

[franco]

Hi,

There is no reason 2.5 or 5 should not work with the cards except varying mileage with the actual modules used as they may or may not work due to technical incompatibilities on either end.

We don't have any recommendation for modules of this range at the moment, sorry.


Cheers,
Franco

[JanW]

Thanks, @franco, for your reply! Good to hear that there is at least a possibility this may work. I guess I'll have to try

EDIT:
Did some more research, and according to a review by servethehome.com (https://www.servethehome.com/sfp-to-10gbase-t-adapter-module-buyers-guide/ ), the Mikrotik module consumes considerably more power than comparable ones. And the generic FS SFP-10G-T module listed as compatible on the DEC750 product page (I think they mean this one: https://www.fs.com/fr/products/74680.html?attribute=113&id=219394 ) seems to also support NBASE-T (so 2.5GBASE-T and 5GBASE-T speeds), according to the Q/A and reviews on that page. So I'll go with that.

[franco]

If you could reply back with your results that would help others having the same issue later a lot.


Thanks,
Franco

[JanW]

Sorry, didn't see your response while I was editing my earlier post. I'll go with the FS module and will report back once I have the module and my fiber installed (a few more weeks).

[meyergru]

I think you are wrong on the NBase-T compatibility for that model, see this reply:

https://www.fs.com/de/answer-question/67920?from=product

[JanW]

This answer puzzled me, too. In fact, the answer confirms that the device will auto-negotiate down to 1G. The rest of the answer may indicate that the module but must must still be plugged into a 10G (SFP+) port, meaning the device is not made to be plugged into an SFP port. The answer to the question right before the one you cite talks about connection to 2.5G and 5G devices, and confirms that these connections should work "in theory": https://www.fs.com/de/answer-question/70100

I have since installed the SFP-10G-T module into my DEC750. It is recognized right away. The OPNSense interface allows me to choose data rates based on auto-detection, or 10G, 1000 and 100 speeds (to be exhaustive: 100M-SGMII, 100baseTX, 1000Base-SGMII, 1000baseT, 1000baseSX, 1000baseLX, 1000baseCX, 1000Base-KX, 10GBase-SFI, 10Gbase-T, 10GBase-KR).

Even though 5G and 2.5G data rates are not listed, the interface allows to connect just fine to the 2.5GbaseT port of my wifi router in the "auto-detect" setting. So this actually does what I intended it to do.

[meyergru]

Good for you. When I looked for a similar device in 2020, there were few that supported 2.5 and 5 GBps.

Ubiquiti sells one, but that gets reportedly too hot. I got one that works like yours, i.e. the intermediate speeds are intransparent to the host. This is O.K. for most cheap 2.5 Gbps counterparts (like Realtek-based chips), but can be problematic for counterparts that also have all speeds.

I found that anything up to 5 Gbps is fine over older CAT5 cabling, whereas 10 Gbps sometimes works but is unreliable. Thus, manual selection would be nice to have...