Hi, I am trying to connect two CRS812 DDQ switches using the 400Gbps ports but the highest speed I am seeing is only 200Gbps for the link. I have tried auto-negotiation and manually configuring the speed on both switches. Supported speed shows 400G-baseCR8 but if I try to configure that manually on both sides, the link goes down. Below is the output from one of the switches. The other one shows the same. I have tried multiple cables which are rated for 400Gbps. One eg. https://marketplace.nvidia.com/en-us/enterprise/personal-ai-supercomputers/qsfp-cable-0-4m-for-dgx-spark/?utm_source=nvidia. Has anyone seen a similar issue?
[admin@MikroTik] > /interface ethernet monitor qsfp56-dd-1-1
name: qsfp56-dd-1-1
status: link-ok
auto-negotiation: disabled
rate: 200Gbps
full-duplex: yes
tx-flow-control: yes
rx-flow-control: yes
fec: fec91
supported: 10M-baseT-half
...
100G-baseSR2-LR2
100G-baseCR2
200G-baseSR4-LR4
200G-baseCR4
400G-baseSR8-LR8
400G-baseCR8
[admin@MikroTik] > /system/resource/print
uptime: 18w23h56m22s
version: 7.19.5 (stable)
build-time: 2025-08-22 11:17:02
factory-software: 7.19.1
free-memory: 3772.4MiB
total-memory: 4096.0MiB
cpu: ARM64
cpu-count: 4
cpu-frequency: 2000MHz
cpu-load: 0%
free-hdd-space: 479.4MiB
total-hdd-space: 512.0MiB
write-sect-since-reboot: 78747
write-sect-total: 78747
bad-blocks: 0%
architecture-name: arm64
board-name: CRS812-8DS-2DQ-2DDQ
platform: MikroTik