Junos OS Commit Model

The router configuration is saved using a commit model: a candidate configuration is modified as desired and then committed to the system. Once committed, the router checks the configuration for syntax errors and if no errors are found, the configuration is saved as juniper.conf.gz and activated. The former active configuration file is saved as the first rollback configuration file (juniper.conf.1.gz) and all other rollback configuration files are incremented by 1. For example, juniper.conf.1.gz is incremented to juniper.conf.2.gz, making it the second rollback configuration file. The router can have a maximum of 49 rollback configurations (1–49) saved on the system.

On the router, the active configuration file and the first three rollback files (juniper.conf.gz.1, juniper.conf.gz.2, juniper.conf.gz.3 ) are located in the /config directory. If the recommended rescue file rescue.conf.gz is saved on the system, this file should also be saved in the /config directory. The factory default files are located in the /etc/config directory.

There are two mechanisms used to propagate the configurations between Routing Engines within a router:

• Synchronization—Propagates a configuration from one Routing Engine to a second Routing Engine within the same router chassis.
  To synchronize a router’s configurations, use the commit synchronize CLI command. If one of the Routing Engines is locked, the synchronization fails. If synchronization fails because of a locked configuration file, you can use the commit synchronize force command. This command overrides the lock and synchronizes the configuration files.
• Distribution—Propagates a configuration across the routing plane on a multichassis router. Distribution occurs automatically. There is no user command available to control the distribution process. If a configuration is locked during a distribution of a configuration, the locked configuration does not receive the distributed configuration file, so the synchronization fails. You need to clear the lock before the configuration and resynchronize the routing planes.

Note: When you use the commit synchronize force CLI command on a multichassis platform, the forced synchronization of the configuration files does not affect the distribution of the configuration file across the routing plane. If a configuration file is locked on a router remote from the router where the command was issued, the synchronization fails on the remote router. You need to clear the lock and reissue the synchronization command.