My guess is that your dhcp client running inside the VM set up the subnet
mask as /128. Dhcpv6 doesn¹t provide prefix length, but the client system
sometime adds the net mask based on the link type. Some of the dhcp
clients use a script to configure the interface, and I think you can use
/64 if your link is ethernet.

‹Robert

On 2/19/15, 4:27 AM, "Andreas Scheuring" <scheu...@linux.vnet.ibm.com>
wrote:

>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-r
>a.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)
>
>
>
>
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