It seems that Sunderland are linked every other day to anyone from the Netherlands who can kick a ball.
The latest instalment is out of contract Ron Vlaar, the defender has played for Aston Villa since 2012, but is now out of contract, not signing a new deal with the midlands club. Thus attracting the attentions of several clubs, and clearly because Sunderland has a Dutch manager there will be the a link.
Sunderland are definitely in the market for defenders, and a player with a lot of premiership experience on a free transfer is a feasible option.