Which command should you use to discard all changes made and return to the active configuration in Junos?

The command used to discard all changes made and return to the active configuration in Junos is "rollback 1." This command reverts the configuration to the last committed state, effectively discarding any uncommitted changes that have been made since the last commit. In the Junos operating system, configurations are changed in a candidate mode where modifications can be made without immediately applying them to the active configuration. Using "rollback 1" cancels any such candidate changes and allows the system to revert back to the previously active (committed) configuration.

In contrast, the choice of "rollback 0" would revert the configuration to the initial factory-installed configuration, which is generally not what is meant when one wishes to discard the last set of changes. The "reset configuration" command is used for different purposes, such as clearing the entire configuration, which would not only discard changes but potentially erase all settings. Similarly, "discard changes" functions to abandon uncommitted changes but does not specifically revert to the last committed configuration, making "rollback 1" the most precise command for this task.