SDN (software-defined networking) promises some real benefits for people who use networks, but to the engineers who manage them, it may represent the end of an era. Ever since Cisco made its first routers in the 1980s, most network engineers have relied on a CLI (command-line interface) to configure, manage and troubleshoot everything from small-office LANs to wide-area carrier networks. Cisco's isn't the only CLI, but on the strength of the company's domination of networking, it has become a de facto standard in the industry, closely emulated by other vendors.