The Cisco-Arista Battle Over CLI

Arista's use of Cisco's command-line interface is at the heart of the legal dispute between networking vendors.

Tom Hollingsworth

February 2, 2016

4 Min Read
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(Editor's note: On Feb. 2, an International Trade Commission judge ruled that Arista infringed on three Cisco patents.) 

The dispute between Arista Networks and Cisco heated up this week. Arista, the target of a lawsuit by Cisco for the past year over claims of copyright and patent infringement, leveled its own countersuit. This countersuit claims that Cisco violated the Sherman Antitrust Act by encouraging the industry to use Cisco's CLI commands as a standard, then turning around and suing companies that embraced that CLI standard.

The term “industry standard CLI” has become universally recognized to mean “Cisco-like CLI.” A simple search of the term brings up results from a variety of different vendors, including Dell, Allied Telesys, and Hewlett Packard Enterprise. Networking vendors have long embraced the Cisco CLI syntax for their networking devices. It makes sense due to the large amount of training material available for the Cisco CLI as well as the learning curve needed to master the environment. Network professionals who are comfortable using a Cisco syntax will be more comfortable using it on a non-Cisco device as opposed to a completely foreign CLI concept like that of Juniper Networks, for example.

At issue is whether Arista copied the CLI too perfectly. In a recent blog post, Cisco pointed out that Arista’s CLI has more than 500 command-line expressions in common with Cisco IOS, far more than any other competitor does. Whether or not Arista copied these CLI commands directly or implemented them in a clean room design is not clear. Even the sound clip in the Cisco post that features Arista CTO Ken Duda claiming “slavish copying” isn’t clear on that point.

What is clear is that Arista sees Cisco as the aggressor in this matter. The Sherman Antitrust Act has been used for more than a century to litigate monopolies and trusts that discourage competition in industries. It has been used against movie studios, telecommunications companies, and even oil companies. While Cisco cannot be said to have a monopoly on the networking market like some of these other Sherman defendants, it could be seen as a trust, which can be defined as “a large business with significant market power”

Arista is hoping to use  violations of the “rule of reason” in this case. Simply put, is Cisco trying to stifle competition by enforcing a patent on its industry-standard CLI? Intent is key to rule-of-reason violations. The court will look at the previous history around the point in question and all the reasons why Cisco has or has not sued in the past for violations of the CLI look-and-feel.

Impact on networking pros

What does this mean for network professionals in the short term? The case isn’t scheduled to go before a judge until August. Even with appeals, countersuits, and legal wrangling, any impact might not be felt for years to come. Cisco is awaiting a ruling from the International Trade Commission (ITC) on its patent claims on Feb. 2. If the ITC rules that Arista has infringed, the company can be penalized. Cisco would then push to have all imports of Arista’s switches halted, which could impact projects scheduled to kick off after that date.

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Should this lawsuit deter you from making a technology decision? I would say not yet. Any projects on the board for completion in the next 90 days won’t be impacted by any rulings in either the ITC case or the California lawsuit. These motions represent positioning from both sides trying to find out how far the opponent is willing to take things. Cisco may very well be upset that Arista copied its CLI too perfectly. Arista is probably angry that it was the one company out of all the competitors to be smacked. But this case is far from resolution.

In the short term, network professionals who use Arista equipment today shouldn’t be worried. Even if there is some kind of decision that goes against Arista, work  can be done to the Arista EOS CLI to reduce the number of common expressions back to a number that Cisco would be comfortable with. If Cisco still pursues these newer EOS versions for copyright infringement, it would open itself  up to a very sticky situation that would require it to sue half of the networking industry in good faith to prove that everyone is copying their CLI. And if winning one lawsuit against your competitor is tough, imagine trying to win 10 at once.

About the Author(s)

Tom Hollingsworth

nullTom Hollingsworth, CCIE #29213, is a former VAR network engineer with 10 years of experience working with primary education and the problems they face implementing technology solutions. He has worked with wireless, storage, and server virtualization in addition to routing and switching. Recently, Tom has switched careers to focus on technology blogging and social media outreach as a part of Gestalt IT media. Tom has a regular blog at and can be heard on various industry podcasts pontificating about the role technology will play in the future.

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