L3 or L2 loopback on MCX4121A-ACAT

Dear All!

i’m trying to check card MCX4121A-ACAT with Viavi MTS 5800 tester. To achieve this, I am trying to set a software loopback on the port of this card. According to the output of mlxlink, this card supports two loopback modes: PH (PHY Local Loopback) and EX (External Local Loopback). The idea is to send a BERT or Acterna sequence to the port of the card, loop it back using the card’s processor, and receive it on the tester for analysis. The speed is low - 10Gbps. I am trying to set the loopback using mlxlink -d /dev/mst/mt4117_pciconf0 -l … followed by the type of loopback(PH or EX). I have tried both EX and PH. The tester does not detect either of these loopbacks. I have tried both with fixed port settings and with auto-negotiation. The tester has been used for many years to test DWDM/SDH/IP/MPLS L2 channels, and I have no doubts about it. It detects as software as hardware loops w/out problems. I am starting to doubt that this card can set the loopback. ICMP ping tests at higher OSI layers work without problems. DDM returns normal signal levels. There are no questions at L1. Please help me understand the situation or point me to the correct manual. Thank you in advance.

mlxlink -d /dev/mst/mt4117_pciconf0

Operational Info

State : Active
Physical state : LinkUp
Speed : 10GbE
Width : 1x
FEC : No FEC
Loopback Mode : External Local Loopback
Auto Negotiation : ON


**Supported Info**
Enabled Link Speed                 : 0x0400701c (10G)
Supported Cable Speed              : 0x00004000 (10G)
**Troubleshooting Info**

Status Opcode                      : 0
Group Opcode                       : N/A
Recommendation                     : No issue was observed

**Tool Information**

Firmware Version                   : 14.32.1010
MFT Version                        : mft 4.30.1-8

These loopback modes are not for looping the packets locally and sending them to the peer (aka PMA loopback)

EX mode == using a loopback module on the local port to loop tx packets back into the port

PH mode == looping packets without going on the wire – from the local TX to RX.

The device you have (CX-4 Lx - MT4117) doesn’t support PMA loopback (RX to TX)