Physical Loopbacks on IB switches

Apologies if this question has been asked before. I am a noob and did search before posing the question.

I’ve a requirement to create an active loopback on an Mellanox SB7700. These are all 100G IB ports. The physical loops, (Amphenol) provided to me will not

activate. The switch appears to completely ignore them. I can, however, dump the eeprom data. So, I know they are “out there” and connected. I am definitely new to IB.

Can I “force” port activation? If “special” loops are required is it possible in some way to request the 7700 ignore the fact they aren’t Mellanox loops? I ask that because

“other” switches I’ve used will ignore certain cable/loopbacks types but undocumented commands exist to disable the “feature”.

Second Question: I read it’s possible to mirror ports on the SB7700? When I try that it appears to be a licensing issue. Is that correct? Basically all I want to do is generate data

and mirror it to the ports for transmit. I am currently using opensm and stress_test. Have written a few loops files. Works fine. But would like to test the switch stand alone (if possible)

Third Question: Is it possible to get a bash shell, or similar on the SB7700? This would make life sooo much easier.

Thanks and regards --jc

Hi John,

Generally speaking, loopback devices for InfiniBand protocol based equipment is not as trivial as looping back few wires towards the port itself. It is a bit more involved due to the nature of paths static routes the IB network.

I am not aware of any loopback device that is available today for IB user testing.

As for the port mirroring capability, it is not supported on this device.

I pretty much did not help you with what you were looking to achieve, but I welcome you to contact Mellanox support and challenge the group. Maybe they can find another way of helping here.



Also, there is no bash shell configuration option on an SB7700 running MLNX-OS.

Configurations can be done vie the CI or via the web GUI.

If you are simply looking for a simple way to test port and cable functionality prior to installing a switch, you can link up a port using this simple process:

  1. Connect two ports on this same switch with a proper 100Gb EDR Mellanox InfiniBand cable

  2. Launch Subnet Manager (OpenSM) process on the switch (config# ib sm,and see it is enabled with “show ib sm”.

  3. The ports will link up and you can view port details with “show interface IB 1/x”, or “show interface IB 1/x counters” (where x is appropriate port #)

IB ports are enabled by default, and no port configuration is needed. Ports and cables are “clean” if you see no errors or discards in the port statistics output.

You can also connect two IB adapter ports to the switch (using 2 cables), and launch OpenSM on a server (or on the switch). Then you can generate traffic on one adapter port and receive it on another.

I hope this helps,

Thanks, Colin