Why do subdomains of all sites on a server redirect to the same site on the same server?

Question

Nginx

Three sites are hosted on a dedicated server (nginx + apache). Redirection from the www subdomain works without problems:
www.aaa.ru > aaa.ru
www.bbb.ru > bbb.ru
www.ccc.ru > ccc.ru
However, all other subdomains are redirected to aaa.ru:
bla.bbb. ru > aaa.ru
xyz.ccc.ru > aaa.ru
In the settings of the DNS records of the server, everything is identical and seems to be correct, there is a
CNAME record *.bbb.ru is an alias of bbb.ru.
What's the catch? nginx settings?

Answer 1

Look at the contents of .htaccess
And read how your whole economy works. DNS is not responsible for redirecting on the site.
DNS lookup - Nginx - Apache (if installed) needs to look at the entire chain.

Answer 2

Because aaa.ru is default_server.

Answer 3

*.bbb.ru is a synonym for all subdomains not explicitly listed in DNS.
+ see configs, webservers. There, carefully on the default server and what subdomains are generally registered on the servers.
In some cases, it is convenient to specify
server_name example.org *.example.org in the web server itself;
what does the domain itself and all its 3rd level domains mean