Internal Mobility at Tier 1 BBs

People who work at GS/MS/JPM - How is internal mobility in Investment Banking across both groups and offices for mid-bucket and up juniors? 

For example, I work at a Tier 2 BB in a Tier 2 city, and there is push for internal mobility from management. After ~1.5 year, you can usually move pretty freely across offices and groups as long as there is an opening (sometimes even without openings for top performers interested in larger groups). Every opening is first offered internally before being posted externally. Of course, the success of the internal move is highly dependent on performance, and sometimes fit.