A likely issue is QSFP speed and adapter compatibility. On DGX Spark, QSFP ports (ConnectX-7) are optimized for validated use cases and QSFP-to-SFP(+) adapters are not officially tested, with reports of the Spark not detecting links unless very specific speeds and settings are forced . On the Jetson AGX Thor side, the QSFP port defaults to 10 GbE and must be explicitly reconfigured for 25 GbE, supporting only one speed at a time via BSP/kernel configuration . If speeds, lane modes, or optics don’t match exactly on both ends, the link simply won’t come up.
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In practice, direct Spark<>Thor QSFP cabling is unlikely to work reliably. The proven approach is to use a switch that explicitly supports 10 GbE or 25 GbE Ethernet on both sides, with validated optics