QSFP & SFP28

[KirkM]

Hi folks,

I have a set of stacked MS355-48x2's and am trying to connect a set of non-cisco TOR aggregate switches that have SFP28 ports.

1. Has anyone tried this? and
2. Were there any specific transceivers that worked if you DID get it to work.

What I'm trying to mix is the aforementioned MS355's with an FS QSFP-IR4 40G transceiver down to a Ubiquiti USW-Pro-Aggregate switch with SFP28 ports. The transceiver used is a native Ubiquiti SFP28 unit. Both with LC/LC connectors. Thoughts?

[CMR]

@KirkM SFP+ and SFP28 are compatible and will run at 10Gb/s. QSFP+ and QSFP28 are also compatible and will run at 40Gb/s.

You cannot generally connect a QSFP to SFP as the former is really just four channels of the latter, though there some adapters that disable three channels to make a 40Gb port run at 10Gb. I don't know whether these work with Meraki switches and I would be surprised if they then work reliably with a SFP28 port, but it could...

The FS module that is most likely to work is: https://www.fs.com/uk/products/72582.html

[zhangqd · Accepted solution]

1. SFP28 is an enhanced version of SFP+. It has the same size as SFP+, but it can support single channel 25Gb/s rate. SFP28 provides an efficient solution for 10G-25G-100G network upgrades to meet the growing needs of next-generation data center networks.
2, QSFP+ package can support four channels at the same time, each channel data rate of 10Gbit/s, through the four channels to achieve 40Gbps transmission rate. Compared with SFP+, the transmission rate of the QSFP+ optical module can be up to four times that of the SFP+ optical module. The QSFP+ optical module can be directly used when a 40 GBIT/s network is deployed, effectively saving costs and improving port density.
3. SFP28 is the encapsulation type of the 25 GBIT/s /32 GBIT/s optical module. QSFP+ is an encapsulation type of the 40 GBIT/s or 56 gbit/s optical module. SFP28 has a single laser and a single detector; The QSFP+ built-in 4-channel laser array and 4-channel detector array encapsulation type of the interface protocol are different
4. Conclusion: The two can not be connected successfully

FS QSFP-IR4-40G

https://cn.fs.com/products/84672.html?attribute=9354&id=314121

[CMR]

As an update the FS module shown above is unlikely to work as it relies on the switch supporting the 1x40Gb -> 4x10Gb splitting mode breakout cables. This is not supported on MS355s or any other Meraki switch apart from perhaps the MS390 as that is a Cisco 9300 and it would work on one of those.

[yanjoe9527]

I think the issue here is less about the brands and more about the signaling mismatch.

You’ve got QSFP+ (40G) on the MS355 side and SFP28 (25G) on the Ubiquiti USW-Pro-Aggregate side, and those don’t really line up cleanly. The 40G IR4 module is basically running 4×10G lanes, while SFP28 is a single 25G lane — so there’s no straightforward way for them to “talk” to each other.

Also yeah, LC/LC doesn’t really help here — that’s just the connector, not the signaling. Easy trap to fall into.

If you want something that actually works, you’ve got a couple of more realistic options:

• Drop both sides down to 10G (SFP+), that’s usually the easiest
• Or use a QSFP+ breakout (4×10G), if the MS355 supports it
• 40G → 25G direct is… pretty much a dead end in most setups

On the optics side, mixing vendors can sometimes add another layer of pain (EEPROM checks, etc.), even if in theory it should work. If you’re testing different modules, it can help to use ones that are coded for multiple platforms or can be customized — something like this as a reference:
https://www.fibermanialink.com/collections/fiber-networking-equipment/high-speed-transceivers/

[CMR]

@yanjoe9527 neither of your suggestions work on native Meraki hardware including the MS355 as breakout cables or single lane cables are not supported.