I have responsibility for a number of Drupal 6 and Drupal 7 sites and I'm curious about a difference I've noted among them.
URL aliasing is enabled on all of the sites, so that a user who navigates to 'some/readable/path' is directed to 'node/123' but continues to see the 'some/readable/path' URL alias in the browser's address bar.
On most of the sites, if the user requests 'node/123', that URL is displayed in the browser's address bar. On a few of the sites, however, the user who enters 'node/123' sees 'some/readable/path' in the address bar.
I was not aware that this sort of "bidirectional aliasing" was possible; it doesn't seem to be default behavior. Is there a module which provides this bidirectional capability? If it is default behavior, how is it enabled?