{% for config in floating_ips %}
{%if 'ipv4' in config %}
auto eth0:{{ loop.index }}
iface eth0:{{ loop.index }} inet static
    address {{ config.ipv4 }}
    netmask 32
{% endif %}
{%if 'ipv6' in config %}
auto eth0:{{ loop.index }}
iface eth0:{{ loop.index }} inet6 static
    address {{ config.ipv6 }}
    netmask 64
{% endif %}
{% endfor %}