Allen, a fifth-year pro, signed a one-year contract. He was limited to two games for the Packers last season by a foot injury that led to his being placed on the Reserve/Injured list on Oct. 2.
The Packers had lukewarm interest in Allen, but after the team selected Justin Harrell with the 16th overall pick of the NFL draft, there was no room for Allen.
Allen also met with the Atlanta Falcons this off-season.
Allen entered the NFL in 2003 as a college free agent with New Orleans, seeing action in 10 games. The New York Giants acquired him on waivers just before the start of the 2004 regular season, and he played for the Giants in five games in '04 and in 14 games in '05.
His career NFL totals include 31 games, three starts, 52 tackles, three sacks and two fumble recoveries. He also saw action in a 2005 postseason game with the Giants, logging three tackles.
Allen is the fifth unrestricted free agent to sign with Cincinnati since the March 2 start of UFA availability. Signing previously were DT Michael Myers of Denver and three UFAs choosing to stay with Cincinnati -- TE Reggie Kelly, DE Justin Smith and RB Kenny Watson. (Smith was also designated as Cincinnati's franchise player).