Difference between router path and link path?

Question

I have recently started looking into the drupal menu system. I am not able to understand the difference between a router_path and the link_path. Both point to the same location in my installation.

Answer 1

Pro Drupal Development, Second Edition describes them as:

menu_links.link_path is the Drupal path or external path this link points to.

menu_links.router_path is for links corresponding to a Drupal path (0 means external), this connects the link to a menu_router.path for joins.