Banana Pi has started selling an inexpensive 2.5Gbps SFP to RJ45 adapter for their Banana Pi BPI-R3 WiFi 6 router board that goes for $17.89 plus shipping ($25 shipped here) on Aliexpress.
The BPI-R3 router includes five Gigabit Ethernet RJ45 ports as well as two 2.5GbE SFP cages, but since not everybody has equipment that takes SFP cables, they used to sell it with a $30 TP-Link adapter. The company now appears to have found a cheaper model marked “SFP-2.5G-T” module that works with their board.
It’s designed to be inserted into one of the 2.5GbE SFP cages and provide a more common 2.5GbE RJ45 port to the user. There’s very little information about the module except its designed with an up to 100-meter cable, and the serial number BT2211010016 only points to Banana Pi’s Wiki. But I don’t think the company designed its own adapter and found another Wiki for the BPI-R3 board that refers to an “SFP-2.5G-T” module of the same name from fs.com. The author of the wiki purchased it for around 50 € in Germany, after failing to have the Mikrotik S+RJ10 1G/2.5G/10G adapter getting recognized by the Banani Pi board.
The design is slightly different so it’s not the same SFP-2.5G-T. While looking at the topic, I found some adapters on Amazon, most of which are for $40 to $50, except one that is sold for $24.99. Some people complain that it does not work with Ubiquiti Aggregation Switch, but as I understand it because the switch is using 10GbE SFP cages, and this type of passive adapter only works at the stipulated speed. In other words, you can connect the SFP-2.5G-T module or similar to a 2.5GbE SFP cage, but it won’t work with 10GbE, 5GbE, or even gigabit Ethernet.
Besides the Banana Pi adapter, it’s also possible to purchase other 2.5Gbps SFP to RJ45 adapters on Aliexpress with a similar price, or a bit lower, and even under $20 shipped per unit if you can purchase a pack of ten (There’s a one-dollar discount with coupon N97EHTBFXV7J).
Jean-Luc started CNX Software in 2010 as a part-time endeavor, before quitting his job as a software engineering manager, and starting to write daily news, and reviews full time later in 2011.
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It’s really inexpensive and could be used to bring a 3rd RJ45 port to a Clearfog or mcbin as well.
By the way the model name “SFP-2.5G-T” is really generic, and I expect that all of them will be called the same way. It’s just <connector>-<speed>-<cable-type>, with “T” for “Twisted pair” like in “1000baseT”, nothing fancy.
The fact that it doesn’t work in other ports is normal. It’s not that the module is passive, it’s that the type of link (and its speed) are indicated by the module itself as SFP was mostly made for fiber and is not supposed to adapt to anything. If anything has to be adaptable, it’s the cage. Some boards or switches support multiple speeds on SFP/SFP+/QSFP+ cages, others not. Thus it will really just depend on the SoC or the phy that’s connected to the cage.
I used one cheap adapter on Clearfog Pro. It didn’t work until I lowered I2C speed to communicate with it. After that it worked like a charm.
Good to know, thanks Peter!
one problem with most 2.5G SFP modules is that their interface towards the board is not well defined in the datasheets. it seems some modules scale up from 1G while others could scale down from 10G (if they support 10G as well). both standards use different line encodings (8b10b vs. 64b66b) and line rates at the same nominal speed
For me SFP normally uses 8b10b and SFP+ 64b66b, so I think 2.5G should be 8b10b (and often it uses the same clock as GbE with a different multiplier, which is not the case for 10G). But it’s true that 2.5G is also a scaled down 10G, so there could indeed be some doubts and confusion.
I have Banana PI3, and almost the same adapter, but 100/1000. The only place that locks the speed to 2.5G is .dts file, where phy mode now is 2500-x. It’s enough to change it to “sgmii”, and the adapter work just fine. By the way mine look veeeeeery very similar, I also bought it through amazon with generic name, and the device that arrived was from that manufacturer https://www.10gtek.com/sfp1g10g
We are now more succesful in using the SFP OEM 2.5G-T module. A patch-set is in the making where the kernel has full control of the Realtek rtl8221b PHY chip on the module. The same amount of control as if the chip is directly mounted on the board.