Connecting 25Gbe (MCX4121A-ACAT) back to back

I have two 25Gbe dual port cards. I have connected them back to back over two pc’s with a direct attach passive copper cable (SFP 28 - compatible with MCP2M00-A003). I have upgraded the firmware version on both the NIC’s to the latest release. flint query output is:

Image type: FS3

FW Version: 14.25.1020

FW Release Date: 30.4.2019

Product Version: 14.25.1020

Rom Info: type=UEFI version=14.18.19 cpu=AMD64,AARCH64

type=PXE version=3.5.701 cpu=AMD64

Description: UID GuidsNumber

Base GUID: 248a0703001e2e92 4

Base MAC: 248a071e2e92 4

Image VSD: N/A

Device VSD: N/A

PSID: MT_2420110034

Security Attributes: N/A

Yet inspite " ip link show" over the interface shows NO-CARRIER.

3: enp1s0f0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000

link/ether 24:8a:07:1e:2e:92 brd ff:ff:ff:ff:ff:ff

4: enp1s0f1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000

link/ether 24:8a:07:1e:2e:93 brd ff:ff:ff:ff:ff:ff

What am I missing ? How to conneced the above two 25gbe interfaces back to back ?Do I need some special cable ?

Thanks in advance.


Hello Nitin,

Many thanks for posting your question on the Mellanox Community.

Based on the information provided, please make sure you use one of validated and supported cables mentioned in the RN of the ConnectX-4 Lx →

You mentioned that you are using a cable which is compatible with the MCP2M00-A003. Is this a Mellanox cable?

You can do the following troubleshooting steps:

  • Do a loopback test on the same adapter. Check if the link comes up without configuring the adapter
  • Force one port on 25G (as we do not support auto-negotiation above 10G speeds. Normally the auto-negotiation is done by a switch which will advertise and force the correct speed). The command for this → # ethtool -s speed 25000 autoneg off

If this does not resolve the issue, please provide the following information

  • Cable p/n and vendor

Many thanks,

~Mellanox Technical Support