<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cli(env, context_id):
 """Request configuration of a tunnel context. This action will update the advancedConfigurationFlag on the context instance and further modifications against the context will be prevented until all changes can be propgated to network devices. """

    manager = SoftLayer.IPSECManager(env.client)
    # ensure context can be retrieved by given id
    manager.get_tunnel_context(context_id)

    succeeded = manager.apply_configuration(context_id)
    if succeeded:
        env.out('Configuration request received for context #{}'
                .format(context_id))
    else:
        raise CLIHalt('Failed to enqueue configuration request for context #{}'
                      .format(context_id))