About ten days ago I moved a site - mostly a Joomla discussion board - to a new server at a different IP address. During a brief scheduled downtime I replicated the content over and completed DNS switchover (via Cloudflare) as usual, and most traffic has followed it - all real users are able to access the site a new location, and what seems like the majority of web crawler requests.
However, I still have web crawlers attempting to access my site at the old IP. And I do mean, specifically by IP address - though they're attempting to crawl valid paths which now exist on the new server. It's primarily GoogleBot though I see a sporadic BingBot or Yahoo Slurp entry as well. Apache logs show 1-2 accesses per minute on the old server.
All three of these bots do most of their crawling on the new server, however.
I've removed the content from the old server, so these requests are met with 404s. Is there a convention for crawlers to somehow index by server IP?
Is there a way to kick them into looking at the new site? Should I actively be trying to redirect them with custom HTTP error codes?