SAN FRANCISCO — Gigamon Inc., a maker of data traffic management software, scored big gains in its market debut Wednesday, notching another win for the Silicon Valley offices of Wilson Sonsini Goodrich & Rosati and Goodwin Procter, which advised the company and the underwriters, respectively. The $128 million initial public offering of 6.8 million shares was priced at $19, the midpoint of the expected range. The stock closed the day at $28.97, a jump of nearly 50 percent.

The Wilson team advising Gigamon included corporate partner and firm vice chairman Jeffrey Saper, partner Rezwan Pavri, special counsel Alexander Phillips and associates Jordan Coleman and Daniel Wong; employee benefits and compensation partner David Thomas and Washington, D.C.-based associate Michael Montfort; and tax partner Ivan Humphreys and of counsel attorney Andrew Bryant, who works in the firm’s Seattle office. Wilson Sonsini’s Palo Alto office has advised eight issuers on IPOs in the past year. Through a spokeswoman, Wilson attorneys declined to comment on the deal, citing the quiet period.