When bridging a 100G link between a MikroTik CCR2216 and a Juniper QFX switch using, in my example, Intel SPTSBP2CLCKV optical transceivers, you will often see valid physical Rx/Tx optical levels while the L2 link remains stubbornly down.
The root cause of this specific vendor interoperability issue is a Forward Error Correction (FEC) mismatch at the coding sublayer.
Unlike lower-speed optics, 100G CWDM4 heavily relies on FEC for signal integrity, and MikroTik and Juniper do not inherently agree on the default negotiation parameters.
The solution is strictly a matter of aligning this configuration.
To bring the link up, you must explicitly configure the Forward Error Correction on the interfaces to FEC91. It is often enough to do it just on the MikroTik.
By hardcoding FEC91 rather than relying on default auto-negotiation, the coding sublayers on both the CCR2216 and the QFX switch synchronize correctly, allowing the protocol layer to transition to an up state immediately.