Cisco Systems is "a strong supporter of open source software" and believes it's "substantially in compliance" with the provisions of the Free Software Foundation's General Public License.

It is therefore "disappointed" that the Free Software Foundation has decided to sue it for alleged violations of the GPL, Cisco said in a prepared statement Monday after the FSF announced its filing.

The dispute flows out of Cisco's acquisition of the privately held Linksys Group in 2003 for $500 million. Linksys had been the target of criticism from open source advocates that it was using GPL code in its routers but not making the source code of the proprietary system that resulted available to its customers, as required by the GPL. The FSF complaint listed the GLIB C library, Coreutils C language utilities, the Readline C code editor, and Wget command for retrieving HTML files, all FSF-originated software, as being used in the Linksys products.

Cisco took steps to bring itself into compliance with the GPL after buying Linksys, "but the Free Software Foundation was never fully satisfied" by its efforts, said Michael Bennett, an intellectual property attorney with Wildman Harrold, a law firm in Chicago and Los Angeles.

Cisco said in its prepared statement: "We have always worked very closely with the FSF and hope to reach a resolution agreeable to the company and the foundation."

In its filing, the Free Software Foundation stated that it had already attempted to resolve outstanding issues through negotiations. "It appears the parties are deadlocked," said Bennett.

Open source licenses have already been tested once in court in the model railroad software case of Jacobsen v. Katzer. Upon appeal, that case decided that the Artistic License, a less frequently used open source license than the GPL, was enforceable in the manner of a copyright license. A violation of a condition of the license amounted to a violation of copyright, and made the violator subject to "injunctive relief" as well as monetary damages.

With teeth established for the Artistic License, the Free Software Foundation brought the case against Cisco with an apparent desire to see the same interpretation applied to the GPL. And that raises the stakes for Cisco, said Bennett.

If Cisco and FSF don't reach an agreement, the substance of the GPL is going to be tested in a U.S. court for the first time. Previous cases testing the GPL were filed on behalf of the authors of BusyBox, a set of Unix utilities issued under the GPL and used in a wide variety of products. In a series of cases over the past two years, BusyBox users have settled cases filed against them by Eben Moglin's Software Freedom Law Center rather than take the cases to court.