Table of Contents

1. Configuring the interface speed
2. Interface description
3. FEC mode
4. How to connect 1G copper to 25G ports

Example model & SONiC version:

• Aurora 830, Aurora 721, Aurora 621, Aurora 615, Aurora 715
• Netberg SONiC: sonic-202012-nb-inno-211121
• Netberg SONiC: sonic-broadcom-202311-20240802

Configuring the interface speed

By CLI:

admin@sonic:~$ sudo config interface speed Ethernet48 100000
admin@sonic:~$ sudo config interface speed Ethernet52 100000

Check the status:

admin@sonic:~$ show interface status | grep 'Ethernet28\|Ethernet60'
Ethernet48  101,102,103,104     100G   9100     rs   Ethernet48  routed      up       up              N/A         N/A
Ethernet52      69,70,71,72     100G   9100     rs   Ethernet52  routed      up       up              N/A         N/A

By editing /etc/sonic/config_db.json file:

    "PORT": {
....
        "Ethernet48": {
            "admin_status": "up",
            "alias": "Ethernet28",
            "autoneg": "1",
            "fec": "rs",
            "index": "7",
            "lanes": "101,102,103,104",
            "mtu": "9100",
            "speed": "100000"
        },
....
}

And reload the config by “admin@sonic:~$ sudo config reload -y”

Interface description

By editing /etc/sonic/config_db.json file:

    "PORT": {
....
        "Ethernet0": {
            "alias": "Eth0(Port0)",
            "lanes": "1,2,3,4,5,6,7,8",
            "speed": "400000",
            "index": "0",
            "subport": "0",
            "admin_status": "up",
            "description": "Uplink_to_Fabric",
            "mtu": "9100"
        },
....
}

And reload the config by “admin@sonic:~$ sudo config reload -y”

Check the status:

admin@sonic:~$ show interface description
 Interface   Oper   Admin   Alias         Description
 ----------- ------ ------- ------------- -------------------
 Ethernet0   up          up Eth0(Port0)   Uplink_to_Fabric
...

Enabling FEC Mode

This section shows a sample port configuration to enable forward error correction (FEC) mode in SONiC.

FEC mode support three options:

rs – Reed-Solomon
fc – FireCode
none – no FEC applied.

25G FEC recommendations

• sometimes cheap optic modules still require FEC.

Having FEC enabled allows using of less expensive optics without significantly impacting network performance.

admin@sonic:~$ sudo config interface fec Ethernet4 none
admin@sonic:~$ show interfaces status
  Interface            Lanes    Speed    MTU    FEC        Alias    Vlan    Oper    Admin             Type    Asym PFC
-----------  ---------------  -------  -----  -----  -----------  ------  ------  -------  ---------------  ----------
  Ethernet4  125,126,127,128     100G   9100   none    Ethernet4  routed    down       up              N/A         N/A

Or edit /etc/sonic/config_db.json file:

    "PORT": {
....
        "Ethernet28": {
            "admin_status": "up",
            "alias": "Ethernet28",
            "autoneg": "1",
            "fec": "rs",
            "index": "7",
            "lanes": "101,102,103,104",
            "mtu": "9100",
            "speed": "100000"
....
}

How to connect 1G copper to 25G ports

With the help of 1/10G RJ45 SFP+ transceivers, we can connect 1G copper infrastructure to a 25G switch.

In this example, Ethernet0 has a 1/10G RJ45 SFP+ transceiver installed. To establish a 1G connection, we need to set the port speed to 10G and disable FEC.

Settings by CLI:

admin@sonic:~$ sudo config interface speed Ethernet0 100000
admin@sonic:~$ sudo config interface fec Ethernet0 none

Check the result:

admin@sonic:~$ sudo show interfaces status
  Interface        Lanes    Speed    MTU    FEC       Alias    Vlan    Oper    Admin            Type    Asym PFC
-----------  -----------  -------  -----  -----  ----------  ------  ------  -------  --------------  ----------
  Ethernet0          113      10G   9100   none   Ethernet0  routed      up       up  SFP/SFP+/SFP28         N/A

Despite indicating 10G speed in SONiC, the connection speed is 1G. 1/10G RJ45 SFP+ transceivers have a PHY controller by design. While the port speed is still 10G, the PHY established the outer connection at 1G speed.