NameVirtualHost 172.20.30.40

<VirtualHost 172.20.30.40>
# Serveur virtuel primaire
DocumentRoot /www/subdomain
RewriteEngine On
RewriteRule ^/.* /www/subdomain/index.html
# ...
</VirtualHost>

<VirtualHost 172.20.30.40>
DocumentRoot /www/subdomain/sub1
ServerName www.sub1.domain.tld
ServerPath /sub1/
RewriteEngine On
RewriteRule ^(/sub1/.*) /www/subdomain$1
# ...
</VirtualHost>

<VirtualHost 172.20.30.40>
DocumentRoot /www/subdomain/sub2
ServerName www.sub2.domain.tld
ServerPath /sub2/
RewriteEngine On
RewriteRule ^(/sub2/.*) /www/subdomain$1
# ...
</VirtualHost>