Rx-To-Tx Loopback Mode Activation; Tool Usage With Nic Vs. Switch (-P Flag) - Nvidia MSTFLINT Documentation

• The local port (it can be shown by the
mstlink –d <device> --port_type PCIE –port 1 –margin –measure_time 10

Rx-to-Tx Loopback Mode Activation

This capability enables Rx-to-Tx remote loopback mode.
Prerequisite
• The port should be disabled and configured with Force mode [Disable the Auto-negotiation]
• Remote loopback is supported for 25G/50G per lane speed
• If the NIC has 2 ports, both ports should be configured with the same speed
To enable Rx-to-Tx remote loopback mode:
1. Disable the port.
mstlink -d /dev/mst/mt4123_pciconf0 –port_state DN
2. Configure the link mode to Force [Disable the Auto-negotiation].
mstlink -d /dev/mst/mt4123_pciconf0 --speeds 100G --link_mode_force
3. Configure loopback with remote loopback [RM].
mstlink -d /dev/mst/mt4123_pciconf0 –loopback RM
4. Enable the port.
mstlink -d /dev/mst/mt4123_pciconf0 –port_state UP
To return to the normal link operation:
1. Disable the port.
mstlink -d /dev/mst/mt4123_pciconf0 –port_state DN
2. Clear the loopback configuration using the "NO loopback" option.
mstlink -d /dev/mst/mt4123_pciconf0 –loopback NO
3. Enable the port.
mstlink -d /dev/mst/mt4123_pciconf0 –port_state UP

Tool Usage with NIC vs. Switch (-p Flag)

When using mstlink on NVIDIA Quantum HDR switch split ports, make sure you use the split formula
below to calculate the port number:
command):
–show_links
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