I've built a CMS that makes it fairly easy for my client to relocate pages in their site hierarchy. This site has all human-readable and intuitive URLs, so moving a page necessarily means that its URL changes. I am storing records of each resource's past URLs in the data store so that requests for bygone URLs are re-routed to their appropriate successors.

I'm warning my clients not to re-arrange the site willy-nilly (for numerous reasons). But nevertheless I suspect there's a chance page moves could get reversed from time to time.

So I'm trying to figure out whether 301 or 302 or 307 redirects should be used when serving up pages to requests for out-of-date URLs.

I understand the value of using 301 for search engine optimization. But my concern is with this system possibly inadvertently making some pages unavailable to some users

QUESTIONS:

1. That is, if the clients move a page at location/URL A to a new location B, then users get the redirect for A to B, and then the clients move the page back to A again, how long can I expect any of those users to keep getting their requests for A redirected to B -- in this case sending them to my friendly 404 page?

2. Is it until an item in their browser history is cleared?

3. Is the redirect somehow cached in routers throughout the internet?

4. How does this work?

5. How long can I expect the 301 redirect to linger out there ?