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S12700 V200R010C00 Configuration Guide - Device Management

This document describes the principles and configurations of the Device Management features, and provides configuration examples of these features.

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
CSS Setup

CSS Setup

A CSS is set up automatically after you use cluster cables to connect two switches, enable the CSS function on the two switches, and restart the switches. The member switches then send CSS competition packets to each other. After the competition, one switch becomes the master switch to manage the entire CSS, and the other becomes the standby switch.

Role Election

The master switch of a CSS is elected based on the following rules:
  1. The switch that starts and enters the single-chassis CSS state first becomes the master switch.

  2. If the two switches start at the same time, the switch with a higher priority becomes the master switch.

  3. If the two switches start at the same time and have the same priority, the switch with a smaller MAC address becomes the master switch.

  4. If the two switches start at the same time and have the same priority and MAC address, the switch with a smaller CSS ID becomes the master switch.


If the master switch is elected because it starts and enters the single-chassis CSS state first, the other joins the CSS using the process described in New Member Join and CSS Merge.

The master MPU of the master switch works as the system master MPU to manage the entire CSS. The master MPU of the standby switch works as the system standby MPU. The standby MPUs of the master and standby switches work as candidate system standby MPUs. Figure 8-5 shows the role election result after a CSS is set up. In this example, SwitchA is elected as the master switch.

Figure 8-5  Role election result in a CSS

Software Version Synchronization

CSS technology provides an automatic software loading mechanism. Member switches do not have to run the same software version, and they can set up a CSS as long as the software versions running on the member switches are compatible with one another. If the software version running on the standby switch is different from that on the master switch, the standby switch downloads the system software from the master switch, restarts with the new system software, and joins the CSS again.

Configuration File Synchronization

CSS technology uses a strict mechanism to synchronize configuration files. This ensures that member switches in a CSS function as a single device.

  • After the standby switch starts, it synchronizes its configuration file with the master switch.
  • When CSS is running, all the configurations performed by users are recorded in the configuration file of the master switch and synchronized to the standby switch.

The configuration file synchronization mechanism ensures that the member switches save the same configuration file. If the master switch fails, the standby switch takes over all services using the same configuration file. After the CSS splits, the configuration of the master switch is not lost even if it is not saved in a timely manner, and the CSS becomes two single-chassis CSSs with the same configuration. In this situation, if a member switch restarts, its unsaved configuration is lost. For details about a CSS split, see CSS Split and MAD.

Configuration File Backup

After a switch enters the CSS state, it automatically backs up its configuration file used in standalone state by adding the extension .bak to the configuration file name. For example, if the original configuration file name extension is .cfg, the backup configuration file name extension is .cfg.bak. In this way, the device can restore the previous configuration after the CSS function is disabled.

If you want to restore the original configuration of a switch after disabling the CSS function, delete the extension .bak from the backup configuration file name, specify this configuration file for next startup, and then restart the switch.

Updated: 2019-12-28

Document ID: EDOC1000142080

Views: 123997

Downloads: 155

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