Allen, 29, is a former second-round pick of the Eagles back in 2010. He spent five years with the Eagles before signing on with the Raiders in 2015. Oakland brought him back on a one-year deal worth $3 million last year.
The Dolphins signed to a one-year, $3.4 million contract this past March.
In 2017, Allen appeared in seven games for the Dolphins and recorded 20 tackles, no interceptions, and a pass defense.