Cisco isn't literally a monopoly. But in the eyes of the law, does it have enough power to misbehave like one?

Arista wants to raise that question in court. Reinvigorating its legal battle with Cisco, Arista filed a countersuit today that accuses the router giant of violating the Sherman Antitrust Act.

The countersuit is also a response to Cisco's copyright claims. The router giant sued Arista in 2014, claiming Arista violated several Ethernet patents. Arista's countersuit doesn't address those, focusing instead on a separate Cisco accusation — that Arista's copying of text commands from Cisco's command-line interface (CLI) constitutes copyright infringement.

Adding to the fun, the case is about to reach a milestone. On Wednesday, the International Trade Commission (ITC) is due to issue an initial determination on some of Cisco's patent accusations. That full ITC action isn't due to be completed until May, but if Wednesday's ruling goes against Arista, it could foreshadow an ITC injunction against Arista's products.

"The Cisco vs Arista legal case just got much more entertaining," consultant Greg Ferro of Packet Pushers noted on Twitter today, using the all-caps hashtag #POPCORN.

Arista doesn't deny using CLI commands — 514 of them, Cisco claims — that come from Cisco's lexicon. But over the years, Cisco has actively encouraged competitors to use CLI's vocabulary, because the company was continually promoting CLI as an industry standard, the countersuit claims.

"For more than ten years, Cisco made representations that led customers and the industry to believe that Cisco either did not have or would not assert any intellectual property rights claims in the CLI commands it used," the counterclaim reads. Cisco even boasted about competitors mimicking CLI, saying it was a sign of customers' familiarity with the language and an indication that Cisco gear would interoperate with competitors', Arista claims.

So, Cisco’s copyright lawsuit, a reversal of "a long-standing policy," is explainable as a “deliberate scheme to use its monopoly power illegally to suppress competition," Arista claims in court documents.

In the colorful language typical of court documents, Arista’s countersuit also calls Cisco's actions “the last resort of an incumbent monopolist who fears competition from more innovative firms.”

Cisco quickly posted a rebuttal on its corporate blog this afternoon, in which General Counsel Mark Chandler called the countersuit “bogus.”

While it’s true that other companies use CLI commands, Arista overdid it, he claims. “They have directly lifted more than 500 multi-word command line expressions. By comparison, networking products from HP [Hewlett Packard Enterprise], Brocade, Alcatel-Lucent, Juniper Networks, and Extreme each have only a small fraction of overlapping commands."

To add a little more fuel to the "monopolist" fire, Arista's countersuit brings up a new topic: Cisco's rates for SmartNet, its customer support program.

"Cisco has punished customers who seek to purchase Ethernet switches from other vendors by increasing the price it charges for the maintenance and service of its products," the countersuit reads.

Calling the practice "coercive," Arista claims it harms Cisco's competition because most customers have an installed base of Cisco gear. The Arista complaint notes that resellers cannot provide bug fixes and patches; only Cisco can, which means customers "predominantly are locked into Cisco's SmartNet contracts."