Elliott Management Corp. hired Moelis & Co. and filed a report from the investment bank to bolster its $21-a-share bid for networking-equipment maker Riverbed Technology Inc. (Nasdaq: RVBD).

Elliott wants Riverbed’s board to open up the company’s books to potential bidders and to maximize the stock price, the New York-based activist shareholder said in a statement today. Elliott owns about 10.5 percent of San Francisco-based Riverbed and the two have been embroiled in a tug-of-war over the past few months about whether the networking-gear provider should be sold. Elliott has offered $21 a share for the company, which Riverbed turned down last month.

Bloomberg News reported earlier this month that buyout firms including Silver Lake Management LLC, Thoma Bravo LLC and KKR & Co. have also informally expressed interest in Riverbed with offers approaching $25 a share, people with knowledge of the process have said.

Riverbed Chief Executive Officer Jerry Kennelly told Bloomberg News on March 4 that the company had received no “credible” offers. He said he would continue to focus on executing the company’s strategy to expand into new markets.

Elliott filed the report from Moelis with the U.S. Securities and Exchange Commission. Elliott’s offer represents a 22 percent premium over the average price target of Wall Street analysts, Moelis said in a 13-page presentation included in the filing.

‘False Reality’

“By publicly denying the buyer interest that has been expressed to the company and by comparing the value of Elliott’s bid to a false reality, Riverbed’s management and board have crossed a line from failing shareholders to actively misleading them as well,” Jesse Cohn, a portfolio manager at Elliott, said in the statement.

Shawn Dainas, a spokesman for Riverbed, declined to comment.

Riverbed’s shares, which closed at $15.11 the day before Elliott disclosed its stake on Nov. 8 and pushed for strategic changes, have since climbed 33 percent. The stock fell less than 1 percent to $20.06 at the close in New York today.

Charles Elson, director of the John L. Weinberg Center for Corporate Governance at the University of Delaware, said Kennelly has no obligation to open Riverbed’s books to bidders.

“The only question is whether the board has decided to sell the company,” Elson said. “Anyone can make any offer they want based on publicly available information, but until the board has said it’s up for sale and is running a process, it’s not for sale.”