Description of configuration options for ipv6

Configuration option=Default value	Description
fixed_range_v6=fd00::/48	(StrOpt) Fixed IPv6 address block
gateway_v6=None	(StrOpt) Default IPv6 gateway
ipv6_backend=rfc2462	(StrOpt) Backend to use for IPv6 generation
use_ipv6=False	(BoolOpt) use ipv6