Hi, I was playing around with the various dhcp/radvd options of neutron. Very helpful was the matrix [1] that describes the combinations of ra and adress mode that can be configured. For dhcpv6-stateful (ra & adress mode) it says: "VM obtains IPv6 address from dnsmasq using DHCPv6 stateful and optional info from dnsmasq using DHCPv6 stateful" [1] --> My assumption was that IP adresses and prefix are assigned via dnsmasq. But going this way, my instances got the right IP-Adress (great) but always the subnetmask /128, although I configured /64. Dumping the traffic and having a look at dnsmasq logs the dhcp process from solicit to reply worked fine. I was using rhel7 for guest and host and dnsmasq 2.68. I googled around and found some hints, that dhcpv6 does not support prefix delegation. Seems like that it is the job of the radvd daemon [2][3][4] Is that true? And if so, what's the use case of configuring dhcpv6-stateful for ra and address mode? [1] http://specs.openstack.org/openstack/neutron-specs/specs/juno/ipv6-radvd-ra.html#rest-api-impact [2] https://lists.isc.org/pipermail/dhcp-users/2012-May/015446.html [3] http://serverfault.com/questions/528387/sending-netmask-and-gateway-route-with-dhcp-for-ipv6 [4] https://supportforums.cisco.com/document/116221/part-1-implementing-dhcpv6-stateful-dhcpv6 -- Andreas (irc: scheuran)