CRS504-4XQ QSFP28 breakout port flapping issues

Hardware MikroTik hardware general
1

I am trying to break out the QSFP28 ports of my CRS504 into multiple 10/25Gb connections. For this I am using 100GBASE-SR4 and 40GBASE-SR4 transceivers and MPO→4xLC breakout cables.

I have auto-negotiation disabled on all interfaces and set the speed to their appropriate 10G/25G-baseSR-LR setting.

Now I am running into the following problem:

  • If one of the 4 10/25G ports of one QSFP interface is not connected to anything, it looks like ROS is re-initializing the entire QSFP module every few seconds and thus dropping the connections on all broken-out ports.
  • I already tried the “Ignore Rx LOS” option as it sounded relevant, but that seems to have no effect
  • If I disable all non-connected (sub)interfaces of the QSFP port in ROS, everything runs stable

I am using cheap no-name transceivers, so I would not be surprised if that is the issue. But as I can work around the issue in software by disabling interfaces, it could also be a ROS issue.

Has anyone experienced similar issues before? The workaround is fine for ports that are permanently connected or disconnected, but not for ports that go to e.g. workstations that are not online all the time.

Edit: I also tried ROS 7.22b3 as it has “sfp - improved initialization and linking for some QSFP modules;” in the changelog, but that has no effect on my issue.

2

Ok looks like the cause were bad (not breakout compatible) QSFP28 transceivers. That’s what you get from buying the cheapest ones from AliExpress.

3

I'm running into the same problem so grabbed a couple of MIKROTIK XQ+85MP01D QSFP28 transceivers, but they are doing the same thing. :frowning:

I get stable 25G as long as I disable the other disconnected sub-ports.

I guess the next thing I need to try is a different MPO to 4 x LC breakout cable.

Would you mind linking to the transceivers and cables you used?

4

I was just working with the cheapest, no-name stuff from AliExpress.

If you see the exact same behavior as I described in my initial post, I doubt the passive MPO cable is the issue here (check you signal levels though)

I haven't worked with genuine Mikrotik QSFP28 transceivers yet, but looking at the specification I don't see anywhere that it claims to support breakout operation. What I learned is, that I had to use transceivers that explicitly mention that they support breakout operation.

5

Hey thanks for replying :slight_smile:

I actually started with aliexpress stuff when I initially ran into this problem. Your post made me think I needed better QSFP28 transceivers, so I decided to buy the XQ+85MP01Ds.

I started with this:

If you could link to anything you are currently using, that would be appreciated. Otherwise I'm just taking stabs in the dark.

EDIT: Added store names in case links die in the future

6

I have some interesting news. Another AliExpress QSFP28 transceiver just came in and this one actually works with the breakout cable (no flapping if one of the sub-ports is down).

ZYOPM QSFP28-100G-SR: https://www.aliexpress.com/item/1005008926114152.html

I'm honestly shocked this works, while Mikrotik's own XQ+85MP01D don't (which cost 4x as much).

These transceivers look identical apart from the sticker.

Mikrotik's show:

Vendor Name: MikroTik
Vendor Part Number: XQ+85MP01D
Vendor Revision: 02
Manufacturing Date: 25-07-21

ZYOPM's show

Vendor Name: OEM
Vendor Part Number: QSFP28-100G-SR4
Vendor Revision: 04
Manufacturing Date: 26-02-07

I'm guessing it's possible I got unlucky and bought old XQ+85MP01D's (rev 02, 2025 date) and there may be newer versions that work?

EDIT: I wonder if QSFP28 transceivers can be updated (like firmware updates?)