[openstack-dev] [Neutron] AGAIN HELP CONFIRM OR DISCUSS:create a port when network contain ipv4 subnets and ipv6 subnets, allocate ipv6 address to the port.

Sridhar Gaddam sgaddam at redhat.com
Wed Jul 22 11:48:05 UTC 2015

Hello ZhaoBo,

The short summary of the BP [1] is that when a network contains an IPv6 
SLAAC/dhcpv6-stateless subnet, we use RADVD daemon to advertise the 
prefix. RADVD deamon periodically advertises the prefix info which is a 
"multicast message" received by all the hosts/VMs on the network. When 
an ipv6-capable host/VM receives this Router Advertisement message, it 
would generate and configure an EUI-64 IPv6 address (derived via the 
prefix and interface MAC address) to its interface.

I understand your concern saying that you only specified an IPv4 address 
for the port but you got IPv6 address as well.
This is because..
1. You have IPv6 subnets as part of the same network
2. The nature in which SLAAC works and is implemented in Neutron.

Basically, even if Neutron does not include the IPv6 address in the port 
information, the VM port would be having the IPv6 address configured on 
its interface. Since the port would anyway have the IPv6 address, 
Neutron includes the IPv6 addresses (i.e., SLAAC/DHCPv6-Stateless) for 
the user to be aware of the list of addresses on the port.

Please note that this behavior is only for IPv6 subnets configured with 
SLAAC/DHCPv6-Stateless and not for DHCPv6 Stateful subnets.

Regarding the floating-ip behavior, the issue is recently fixed with the 
following patch - https://review.openstack.org/#/c/198908/


On 07/22/2015 04:35 PM, zhaobo wrote:
> Hi ,
> Could anyone please check the bug below? I had received message from 
> some kind people, but I didn't get the answer which i want.
> The key point is why the created port with specify ipv4 subnet as 
> fixed-ip get an ipv6 addr when there are some ipv6 slaac/dhcpstateful 
> subnets.
> And I know the slaac subnet will automatic allocate an ipv6 addr. 
> Users may be confused about this behavior.
> https://bugs.launchpad.net/neutron/+bug/1467791
> This bug description:
> When the created network contains one ipv4 subnet and an ipv6 subnet 
> which turned on slaac or stateless.
> When I create a port use cmd like:
> neutron port-create --fixed-ip subnet_id=$[ipv4_subnet_id] 
> $[network_id/name]
> The specified fixed-ip is ipv4_subnet, but the returned port contained 
> the ipv6 subnet.
> If user just want a port with ipv4 , why returned port had allocated 
> an ipv6 address.
> And I know this is an design behavior from 
> http://specs.openstack.org/openstack/neutron-specs/specs/kilo/multiple-ipv6-prefixes.html#proposed-change
> But we are still confused about this operation.
> And when we create floatingip and the external network just contained 
> an ipv6 slaac subnet, the port will contained the ipv6 addr . Are 
> there some issues ?
> Thank you anyone could help for confirm this issue , and wish you 
> return the message asap.
> ZhaoBo
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