We would like to use a 100GbE to 4x25GbE breakout cable where:
Could you point me to the relevant documentation, please?
Thank you for posting your question on the Mellanox Community.
Based on you request, unfortunately Mellanox adapters do not have the capability to split their ports.
Port-splits is always done from the switch side.
So you can split a 100GbE switch port into 4x25GbE to gain an additional 3 more ports to connect to end-point.
For example → https://community.mellanox.com/s/article/mellanox-breakout-cables-40g–gt–4x10g-and-100g–gt–4x25g
~Mellanox Technical Support