By default, Apache will listen on all IPs, both IPv6 and IPv4.
This is controlled by the Listen directive:
root@localhost ~ # egrep -r Listen /etc/apache2 ... /etc/apache2/ports.conf:Listen 80 ... root@localhost ~ #
To turn off IPv6 in Apache, just change the Listen directive to:
This will limit Apache to listening only to IPv4 connections. Repeat this for port 443 if you want to stop Apache from listening for HTTPS on IPv6.