Unique identifiers

Regardless of how you configure (or change) the path alias configuration for a particular node, you can always get to it if you know its node ID. Node ID numbers (nid) are assigned in order as nodes are created: the first node you create on the site has the ID 1, the second is 2, etc. Node IDs are unique within your site, and there is no way to change the node ID for a given node, short of deleting and recreating it. It may be tempting to try to treat node IDs as reliable, persistent identifiers.