Wilson Sonsini Goodrich & Rosati, Cooley, and several former Cooley partners now at Weil, Gotshal & Manges are advising on Riverbed Technology’s $993.3 million cash-and-stock acquisition of network optimization software provider Opnet Technologies.

The deal, which was announced Monday as Hurricane Sandy lashed the northeastern U.S., represents a merger of software companies based on opposite coasts. Bethesda, Md.-based Opnet will be folded into San Francisco-based Riverbed’s Cascade business unit, according to The Associated Press.

Opnet has turned to Cooley corporate partners Jennifer DiNucci and Brent Siler in Palo Alto, Calif., and Reston, Va., respectively, for outside M&A and finance counsel on the sale to Riverbed. (Siler joined Cooley in January 2008 from Wilmer Cutler Pickering Hale and Dorr, where he spent more than 20 years.)

A team of lawyers from Wilson Sonsini and Weil, meanwhile, are representing Riverbed, whose acquisition of Opnet will allow the company to expand its network performance management business while moving into the application performance management market, according to a press release announcing the transaction.

Leading Weil’s team on the transaction are M&A partners Keith Flaum and James Griffin; technology transactions partner John Brockland; banking and finance partner Danek Freeman; capital markets partner Jennifer Bensch; and tax partner Helyn Goldstein. (Bensch joined Weil in January from Skadden, Arps, Slate, Meagher & Flom, where she was a partner in the firm’s financial institutions practice and took the lead representing underwriters on an initial public offering earlier this year for private equity giant The Carlyle Group.)

Flaum and Brockland were once partners at Cooley before they left that firm in the summer of 2009 to join Dewey & LeBoeuf. Amid Dewey’s collapse earlier this year, Flaum and Brockland joined Weil and brought along Griffin, according to a report at the time by sibling publication The Recorder.

Wilson Sonsini corporate partners David Segre and Richard Blake and antitrust partner Scott Sher are serving as general corporate counsel to Riverbed on the transaction. Riverbed’s general counsel is Brett Nissenberg; Ryan Damon acts as the company’s associate general counsel.

Riverbed’s acquisition of Opnet is expected to close before year’s end.