nginx config catches domains not specified in server_name - nginx

Question

I have two configs enabled in my nginx sites-enabled folder.
The first one (my-domain.fr.conf) looks like this:
server {
listen 443 ssl http2;
server_name my-domain.fr;
index index.html;
location / {
root /www/my-domain.fr;
}
include ssl_certif.conf;
}
# HTTP redirect
server {
listen 80 default_server;
server_name my-domain.fr;
location / {
return 301 https://my-domain.fr$request_uri;
}
}
The second one (sub.my-domain.fr.conf) looks like this:
server {
location / {
proxy_pass http://127.0.0.1:8080;
}
include ssl_certif.conf;
server_name sub.my-domain.fr;
listen [::]:443 ssl;
}
server {
if ($host = sub.my-domain.fr) {
return 301 https://$host$request_uri;
}
server_name sub.my-domain.fr;
listen [::]:80;
return 404;
}
I would expect the last one to only catch requests to sub.my-domain.fr subdomains, but instead it catches anything (I have wildcards subdomains set up on my DNS), and even masks my-domain.fr.
How can I make sure it only catches sub.my-domain.fr requests?

Answer 1

I found the reason.
sub.my-domain.fr supports ipv6 (listen [::]:443 ssl;). my-domain.fr doesn't.
I suppose my connection is using ipv6 when it can, and in this case, sub.my-domain.fr is the only match.
Adding ipv6 support (listen 443 ssl => listen [::]:443 ssl;, and listen 80; => listen [::]:80;) in all server entries fix it.