DEC840 SFP+ support for 5gbit? (axgbe driver)

[feld]

I'm looking at the source of the axgbe driver and it appears it supports 10/100/1000/2500/10000 but interestingly enough 5000 is missing.

https://github.com/opnsense/src/blob/stable/23.1/sys/dev/axgbe/if_axgbe_pci.c#L2286-L2311


Is this a limitation of the hardware? With a few source changes could it work with e.g., this SFP+? https://www.fs.com/products/173216.html

I don't have a test env for this yet but I'm thinking of a scenario where I may want 5gbit support here (with AT&T fiber)

[tuto2]

No, the hardware doesn't support 5gbit (and 2.5gbit is also not applicable for any DEC product, the official axgbe "mode" is exclusively meant for backplane connections). That being said, copper based SFP+ modules are often smart and are capable of negotiating their own speeds based on the port speed of the link partner. This means that if you plug in a capable NBASE-T module, the axgbe driver will correctly report it as a 10Gbit module, even though the real link speed will be based on the other end. At this point, the throughput will be limited to either 1/2.5/5/10.

The only module that is capable of doing this that has been tested and verified is https://www.uptimed.nl/producten/transceivers/sfp+/media-converter/UP-TR-10G-RJ45-UNI. But you're free to try the FS module, which I expect won't give any trouble, no guarantees given though.

As part of the limitations, don't expect mixing 1 2.5/5 module and another 10gbit module to work, differing base frequencies are not supported.

[feld]

> That being said, copper based SFP+ modules are often smart and are capable of negotiating their own speeds based on the port speed of the link partner.

Thank you for this tip!