How permanent are 301 permanent redirects?

Question

If www.something.com/here/there/Default.aspx is set to permanently redirect the user to www.something.com/redirect/Default.aspx, but then that permanent redirection is removed, should requests to www.something.com/here/there/Default.aspx still be redirecting?

Even after browser cache is cleared?

Would the servers handling the requests be caching the redirects themselves if they see that there is a permanent redirect on something, and then never refresh that cache?

Answer 1

It is legal for a cache (serverside, on a proxy, or clientside) to permanently store a 301 and automatically redirect forever, but most will not do so.

Internet Explorer 9 was the first browser to permanently cache a 301 that didn't contain any other caching directives, but even that will only last until the browser's cache is cleared.