How do you redirect from a subdomain to another subdomain when the first site is down?

Question

URL Handling

Hello everyone! I came across an interesting question, there is a site like "test.site.ru" if you open it directly through incognito or just through a browser where you have not opened this site before - it says that the site has been deleted. Then we go to the search, we find the same site on request, which is in Google, Yandex, rabmler, mail, bing, I checked all the search engines. We go to the site "test.site.ru" from any search engine, there is a redirect to "test1.site.ru" question?) I open the redirect check service, no redirects were found. Perhaps this is some kind of hidden redirect, not of the usual type, as you specify in .htaccess. I'm breaking my head)) please share your ideas on how this could be done ..

Answer 1

https://en.wikipedia.org/wiki/HTTP_referer
https://www.google.com/search?q=redirect+based+on+...