MikroTik QSFP+ Modules

Hi guys,

our school is planing to get the MikroTik CRS354 Switch with 48 PoE Ports. We need a few of those, each installed in a seperate physical location in the school buildings. I want to link them via QSFP+. We have optic fibre cable runs between those racks. But no one in the school is able to tell me whether these seperate runs are 150 Meters or shorter. They assume it is close, maximum 200 Meters.

My Question: Those MikroTik QSFP+ Modules (MikroTik Q+85MP01D) are rated for connections up to 150 Meters. Does that mean everything over 150 Meters will not connect or is it just, that they don’t connect with the full 40 GB/s? And by the way, those are able to get LC fiber optic connectors, right?

It’s a gamble based on the quality of the fiber and terminations mostly. In a PERFECT install with super clean terminations you might get the maximum distance, or even a bit more. Dealing with a similar issue in one of my building, a run of fiber is just beyond the rated distance.

Otherwise you’ll start seeing errors, malformed packets, drops, etc. You’ll probably still get a link, but it might not be usable due to excessive errors.

I read a blog post about using LX single mode optics on multimode cable, with a mode conditioning (offset) cable to push a bit harder. It’s totally outside of spec but they guys in the post got it to work. Tempted to try the same myself.

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Found this one that claims it’ll push 40gig over 400m of multimode cable


There are some proprietary transceiver types that allow this. 40GBASE-SR4 transceivers have an MPO connector. You’ll have to pay attention to what kind you’re ordering.

Alternately if you have enough fiber cores running between locations, you can use MPO to LC breakout cables on each end, as long as you arrange them in the correct order.

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Are you 100% sure you’re dealing with multimode / 850nm OM4?

For ~35 per SR4 transceiver you might get lucky and get more than 150m?

How much of a pain would it be to pull a singlemode down the same route?

It might make future upgrades easier on the account of you might just pull more than a single fiber pair and then there’s even affordable cwdm options for those wavelengths. - they might be open to the idea of investing into that.

To be honest I’m a bit surprised that the spec range for 40gbase-sr4 is 150 metres.

10gbase-sr has a range of 400m (on om4 fibre), and my understanding is that QSFP+ ports can be split into four 10gb ports (and basically work by bundling 4 10gb links) I would have thought that, worst case, you could split your 40gb link into 4x10gb links that you can team for the same overall bandwidth.

To be honest though it is hugely unlikely that you need that sort of bandwidth on your network - I’d suggest monitoring what you are actually using on a couple of existing switches before you get too attached to the idea of 40gb uplinks on 48 port switches.

Just for context, school I work at we had a nightmare day where some work on the field severed our main fibre between blocks, taking everything down. Thankfully we had an old fibre to fall back on and over the course of a few hours we managed to repatch everything over a single gigabit link, with switches on that block daisy chained off each other, instead of the usual 10gb links to the various cabs.

Nearly half the school was running over this single gigabit link (and we’re a very large school - you’re still taking 200 plus computers supported over this link).

I thought it would be a nightmare, ip phonecalls dropping out, slow access, logon failures, the works.

Instead it was completely fine, didn’t have a single report of anything going slow or not working, and it was like that for weeks while we got someone out to splice the multicore fibre.

Yeah, I noticed that MPO connector. I’m new to the fibre optic topic, and if I identify this correctly, we only have SC connectors on our patchpanels. Is there a solution to go from MPO to SC? Or is it better to change to LC patchpanels (if they exists)?

Not exactly. SC and LC connectors provide a pair of fiber cores, Tx and Rx. MPO is a high-density connector. An MPO connector has positions for 12 or 24 fiber cores (MPO-12 and MPO-24, respectively), although some cables will have fewer cores, depending on the intended use.

QSFP+ transceivers have four “lanes” of Ethernet which each run at a 10 Gbps rate, and these are combined into a single 40 Gbps logical interface. Many switches can also be configured to break out the QSFP+ port into 4x 10 Gbps interfaces. So the 40GBASE-SR4 transceiver needs 8 fiber cores, a Tx and Rx for each lane. Hence an MPO-12 connector is used. In order to adapt that MPO connector to SC, you’ll need a patch cable with an MPO connector on one end and four SC connectors on the other end.

In order to run multiple signals over a single fiber, you have to use different wavelengths of light for each signal (generally described as “wavelength-division multiplexing,” or WDM). So for a QSFP+ transceiver to use an LC connector there are two general approaches. A 40GBASE-SWDM4 transceiver will use four wavelengths and transmit 4 signals out one fiber and receive 4 signals on the other fiber. A “BiDi” or bidirectional transceiver only uses two wavelengths, but it transmits and receives in both wavelengths on each fiber.

It is very easy to go from LC to SC, you just need a patch cable with an LC connector on one end and an SC connector on the other, so it’s not worth the expense of re-terminating fiber in order to do that.

Or you can go over a MPO fanout cable to 4 LC/SC connectors and plug them into 4 different ports on the patchpanel, right?

But I’m tended to go with Ruklaw, I don’t know wether a school network needs 40 GB/s speed.

Is there a 10gbit link in place already, and it’s showing signs of congestion?

No, we at the moment we have old switches with SFP Ports / 1 GB/s and one of them is already dead, on one of them the fan LED is blinking red. So we decided to replace them. And the new ones happen to have those SFP+ an QSFP+ ports.

At the moment it is not possible for a whole class to watch Youtube videos at the same time in 360p. In the future we want to deploy a media server with plex in this network, so my thought was to get the highest bandwidth possible.