You need to undo the active router configuration and return to a previous configuration.
The rollback configuration mode command loads a previous router configuration as the candidate configuration:
 aviva@router1# rollback 1 load complete  aviva@router1# show  aviva@router1# commit commit complete
You can reload any of the previously committed versions of the configuration file. You identify the version by the number, which is the number in the filename. In this example, we reload the last saved configuration file, /config/juniper.conf.1.gz. The rollback command only loads the configuration, making it the candidate configuration, but does not activate it. The commit command activates the retrieved configuration. While using the show command here is optional, it's good practice to verify that the configuration you loaded is what you expect.
To figure out which previous configuration you want to retrieve, you can use a few commands that we have already discussed, including show system commit and file list detail /config. You can use the file list detail /var/db/config command to find out when the older configuration files were activated and by whom. You can also see this information when you issue the rollback command by using the router's built-in help:
 aviva@router1# rollback ? Possible completions: <[Enter]> Execute this command 0 2005-02-25 12:31:52 PST by aviva via cli 1 2005-02-25 10:45:12 PST by aviva via cli commit at 2 2005-02-25 03:10:21 PST by root via cli … 48 2005-02-19 03:01:04 PST by root via cli 49 2005-02-18 18:24:21 PST by aviva via cli | Pipe through a command
Recipes 1.10, 1.14, and 1.18
Router Configuration and File Management
Basic Router Security and Access Control
Routing Policy and Firewall Filters