"It's not obsolete by any definition," Mimms said. He compared SDN to driving a car and CLI to getting under the hood and working on it. For example, for any given set of ACLs (access control lists) there are almost always problems for some applications that surface only after the ACLs have been configured and used, he said. A network engineer will still have to use CLI to diagnose and solve those problems.
However, SDN will cut into the use of CLI for more routine tasks, Mimms said. Network engineers who know only CLI will end up like manual laborers whose jobs are replaced by automation. It's likely that some network jobs will be eliminated, he said.
This isn't the first time an alternative has risen up to challenge the CLI, said Walter Miron, a director of technology strategy at Canadian service provider Telus. There have been graphical user interfaces to manage networks for years, he said, though they haven't always had a warm welcome. "Engineers will always gravitate toward a CLI when it's available," Miron said.
Even networking startups need to offer a Cisco CLI so their customers' engineers will know how to manage their products, said Carl Moberg, vice president of technology at Tail-F Systems. Since 2005, Tail-F has been one of the companies going up against the prevailing order.
It started by introducing ConfD, a graphical tool for configuring network devices, which Cisco and other major vendors included with their gear, according to Moberg. Later the company added NCS (Network Control System), a software platform for managing the network as a whole. To maintain interoperability, NCS has interfaces to Cisco's CLI and other vendors' management systems.
CLIs have their roots in the very foundations of the Internet, according to Moberg. The approach of the Internet Engineering Task Force, which oversees IP (Internet Protocol) has always been to find pragmatic solutions to defined problems, he said. This detailed-oriented "bottom up" orientation was different from the way cellular networks were designed. The 3GPP, which developed the GSM standard used by most cell carriers, crafted its entire architecture at once, he said.
The IETF's approach lent itself to manual, device-by-device administration, Moberg said. But as networks got more complex, that technique ran into limitations. Changes to networks are now more frequent and complex, so there's more room for human error and the cost of mistakes is higher, he said.
"Even the most hardcore Cisco engineers are sick and tired of typing the same commands over and over again and failing every 50th time," Moberg said. Though the CLI will live on, it will become a specialist tool for debugging in extreme situations, he said.
"There'll always be some level of CLI," said Bill Hanna, vice president of technical services at University of Pittsburgh Medical Center. At the launch earlier this year of Nuage Networks' SDN system, called Virtualized Services Platform, Hanna said he hoped SDN would replace the CLI. The number of lines of code involved in a system like VSP is "scary," he said.
On a network fabric with 100,000 ports, it would take all day just to scroll through a list of the ports, said Vijay Gill, a general manager at Microsoft, on a panel discussion at the GigaOm Structure conference earlier this year.
"The scale of systems is becoming so large that you can't actually do anything by hand," Gill said. Instead, administrators now have to operate on software code that then expands out to give commands to those ports, he said.
Faced with these changes, most network administrators will fall into three groups, Gartner's Skorupa said.