How to configure the port breakout in SONiC?

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Introduction

Welcome to the STORDIS Support Portal guide!

This article explains how to manually configure port breakout in SONiC by modifying the port_config.ini file. This method is essential for platforms that use static configuration to split high-speed ports (e.g., 100G) into multiple lower-speed channels (e.g., 4x25G).

Prerequisites

• Access to the SONiC switch via console or SSH
• Administrator or root privileges

• Basic knowledge of the Vim text editor

   

Step-By-Step Guide

Follow these steps to configure port breakout by editing the underlying configuration files:

STEP 1: Navigate to your hardware configuration directory e.g.

admin@sonic:~$ cd /usr/share/sonic/device/x86_64-accton_as7712_32x-r0/Accton-AS7712-32X/

Note: The exact path may vary depending on your installation, but typically it resides in the directory named after your switch model.

STEP 2: Edit the port_config.ini file.

Open the file using Vim:

admin@sonic:~$ sudo vim port_config.ini

Locate the port you wish to break out. You must redefine the lanes and speed for each sub-port.

Example: Breaking out Ethernet0 (100G) into 4x25G

Change this:

Into this:

To save and exit in Vim, press Esc, type :wq, and press Enter.

STEP 3: Apply the changes to the Configuration Database.

After saving the file, you need to adjust the file config_db.json to match the port_config.ini file:

admin@sonic:~$ sudo vim /etc/sonic/config_db.json

Change this:

"PORT": {
       "Ethernet0": {
           "admin_status": "up",
           "alias": "Eth1(Port1)",
           "autoneg": "off",
           "dhcp_rate_limit": "300",
           "index": "1",
           "lanes": "49,50,51,52",
           "mtu": "9100",
           "speed": "100000",
           "subport": "0"
       },

Into this:

"PORT": {
       "Ethernet0": {
           "admin_status": "up",
           "alias": "Eth1(Port1)",
           "autoneg": "off",
           "dhcp_rate_limit": "300",
           "index": "1",
           "lanes": "49",
           "mtu": "9100",
           "speed": "25000",
           "subport": "0"
       },
       "Ethernet1": {
           "admin_status": "up",
           "alias": "Eth1(Port1)",
           "autoneg": "off",
           "dhcp_rate_limit": "300",
           "index": "1",
           "lanes": "50",
           "mtu": "9100",
           "speed": "25000",
           "subport": "0"
       },
       "Ethernet2": {
          "admin_status": "up",
          "alias": "Eth1(Port1)",
          "autoneg": "off",
          "dhcp_rate_limit": "300",
          "index": "1",
          "lanes": "51",
          "mtu": "9100",
          "speed": "25000",
          "subport": "0"
      },
       "Ethernet3": {
          "admin_status": "up",
          "alias": "Eth1(Port1)",
          "autoneg": "off",
          "dhcp_rate_limit": "300",
          "index": "1",
          "lanes": "52",
          "mtu": "9100",
          "speed": "25000",
          "subport": "0"
      },

To save and exit in Vim, press Esc, type :wq, and press Enter.

STEP 4: After saving the file, you need to reload the configuration so SONiC can rebuild the config_db.json:

admin@sonic:~$ sudo config reload -y

STEP 5: Verify the new port configuration.

admin@sonic:~$ show interfaces status

Check if the interfaces (e.g., Ethernet0 through Ethernet3) are present and reporting the correct speed (25000).

STEP 6: Save the running configuration.

admin@sonic:~$ sudo config save -y

Useful links:

Official SONiC Wiki: How to breakout a port

STORDIS Support Portal FAQ