For a variety of byzantine reasons, the iprb driver has never been open sourced, even though everyone who's ever actually had anything to do with it agrees that it should be. (I blame the lawyers on this one...)
So I went ahead and reimplemented -- from scratch -- a new iprb driver. I'd certainly appreciate feedback on the code, which you can read in the webrev. I'm hoping to integrate this into illumos later this week.