Better document router requirements for IPv6
In order for IPv6 to function correctly for instances, a router must be created and added to a subnet. Update the documentation to better highlight this as it wasn't clear a router was required on an isolated subnet such that Router Advertisements messages would be sent. Change-Id: I4aca67c98ae77bbc4c130764af5a92515b95443a Closes-bug: #1886116
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Brian Haley
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@ -4,7 +4,8 @@
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IPv6
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====
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This section describes the following items:
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This section describes the OpenStack Networking reference implementation
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for IPv6, including the following items:
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* How to enable dual-stack (IPv4 and IPv6 enabled) instances.
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* How those instances receive an IPv6 address.
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@ -67,12 +68,12 @@ advertisements for a subnet.
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The IPv6 Protocol uses Internet Control Message Protocol packets
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(ICMPv6) as a way to distribute information about networking. ICMPv6
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packets with the type flag set to 134 are called "Router
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Advertisement" packets, which contain information about the router
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Advertisement" messages, which contain information about the router
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and the route that can be used by guest instances to send network
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traffic.
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The ``ipv6_ra_mode`` is used to specify if the Networking service should
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generate Router Advertisement packets for a subnet.
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generate Router Advertisement messages for a subnet.
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ipv6_ra_mode and ipv6_address_mode combinations
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-----------------------------------------------
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@ -212,24 +213,24 @@ IPv6 supports three different addressing schemes for address configuration and
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for providing optional network information.
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Stateless Address Auto Configuration (SLAAC)
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Address configuration using Router Advertisement (RA).
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Address configuration using Router Advertisements.
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DHCPv6-stateless
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Address configuration using RA and optional information
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Address configuration using Router Advertisements and optional information
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using DHCPv6.
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DHCPv6-stateful
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Address configuration and optional information using DHCPv6.
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OpenStack can be setup such that OpenStack Networking directly
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provides RA, DHCP
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provides Router Advertisements, DHCP
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relay and DHCPv6 address and optional information for their networks
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or this can be delegated to external routers and services based on the
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drivers that are in use. There are two neutron subnet attributes -
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``ipv6_ra_mode`` and ``ipv6_address_mode`` – that determine how IPv6
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addressing and network information is provided to project instances:
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* ``ipv6_ra_mode``: Determines who sends RA.
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* ``ipv6_ra_mode``: Determines who sends Router Advertisements.
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* ``ipv6_address_mode``: Determines how instances obtain IPv6 address,
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default gateway, or optional information.
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@ -258,10 +259,10 @@ When using SLAAC, the currently supported combinations for ``ipv6_ra_mode`` and
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- Address are assigned using EUI-64, and OpenStack Networking
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provides routing.
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Setting ``ipv6_ra_mode`` to ``slaac`` will result in OpenStack Networking
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routers being configured to send RA packets, when they are created.
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This results in the following values set for the address configuration
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flags in the RA messages:
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Setting SLAAC for ``ipv6_ra_mode`` configures the neutron
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router with an radvd agent to send Router Advertisements. The list below
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captures the values set for the address configuration flags in the Router
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Advertisement messages in this scenario.
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* Auto Configuration Flag = 1
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* Managed Configuration Flag = 0
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@ -269,12 +270,18 @@ flags in the RA messages:
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New or existing neutron networks that contain a SLAAC enabled IPv6 subnet will
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result in all neutron ports attached to the network receiving IPv6 addresses.
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This is because when RA broadcast messages are sent out on a neutron
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network, they are received by all IPv6 capable ports on the network,
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This is because when Router Advertisement messages are multicast on a
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neutron network, they are received by all IPv6 capable ports on the network,
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and each port will then configure an IPv6 address based on the
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information contained in the RA packet. In some cases, an IPv6 SLAAC
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address will be added to a port, in addition to other IPv4 and IPv6 addresses
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that the port already has been assigned.
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information contained in the Router Advertisement messages. In some cases, an
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IPv6 SLAAC address will be added to a port, in addition to other IPv4 and IPv6
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addresses that the port already has been assigned.
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.. note::
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If a router is not created and added to the subnet, SLAAC addressing will
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not succeed for instances since no Router Advertisement messages will
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be generated.
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DHCPv6
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------
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@ -291,16 +298,16 @@ follows:
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- Result
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* - DHCPv6-stateless
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- DHCPv6-stateless
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- Addresses are assigned through RAs (see SLAAC above) and optional
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information is delivered through DHCPv6.
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- Addresses are assigned through Router Advertisements (see SLAAC above)
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and optional information is delivered through DHCPv6.
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* - DHCPv6-stateful
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- DHCPv6-stateful
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- Addresses and optional information are assigned using DHCPv6.
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Setting DHCPv6-stateless for ``ipv6_ra_mode`` configures the neutron
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router with radvd agent to send RAs. The list below captures the
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values set for the address configuration flags in the RA packet in
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this scenario. Similarly, setting DHCPv6-stateless for
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router with an radvd agent to send Router Advertisements. The list below
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captures the values set for the address configuration flags in the Router
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Advertisement messages in this scenario. Similarly, setting DHCPv6-stateless for
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``ipv6_address_mode`` configures neutron DHCP implementation to provide
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the additional network information.
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@ -309,9 +316,9 @@ the additional network information.
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* Other Configuration Flag = 1
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Setting DHCPv6-stateful for ``ipv6_ra_mode`` configures the neutron
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router with radvd agent to send RAs. The list below captures the
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values set for the address configuration flags in the RA packet in
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this scenario. Similarly, setting DHCPv6-stateful for
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router with an radvd agent to send Router Advertisements. The list below
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captures the values set for the address configuration flags in the Router
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Advertisements messages in this scenario. Similarly, setting DHCPv6-stateful for
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``ipv6_address_mode`` configures neutron DHCP implementation to provide
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addresses and additional network information through DHCPv6.
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@ -319,6 +326,12 @@ addresses and additional network information through DHCPv6.
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* Managed Configuration Flag = 1
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* Other Configuration Flag = 1
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.. note::
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If a router is not created and added to the subnet, DHCPv6 addressing will
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not succeed for instances since no Router Advertisement messages will
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be generated.
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Router support
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~~~~~~~~~~~~~~
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@ -345,16 +358,17 @@ modified so that an IPv6 subnet is not required for the external network that
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is associated with the neutron router. The LLA address of the upstream router
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can be learned in two ways.
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#. In the absence of an upstream RA support, ``ipv6_gateway`` flag can be set
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#. In the absence of an upstream Router Advertisement message, the
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``ipv6_gateway`` flag can be set
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with the external router gateway LLA in the neutron L3 agent configuration
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file. This also requires that no subnet is associated with that port.
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#. The upstream router can send an RA and the neutron router will
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automatically learn the next-hop LLA, provided again that no subnet is
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#. The upstream router can send a Router Advertisement and the neutron router
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will automatically learn the next-hop LLA, provided again that no subnet is
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assigned and the ``ipv6_gateway`` flag is not set.
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Effectively the ``ipv6_gateway`` flag takes precedence over an RA that
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is received from the upstream router. If it is desired to use a GUA
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next hop that is accomplished by allocating a subnet to the external
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Effectively the ``ipv6_gateway`` flag takes precedence over a Router
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Advertisements that is received from the upstream router. If it is desired to
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use a GUA next hop that is accomplished by allocating a subnet to the external
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router port and assigning the upstream routers GUA address as the
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gateway for the subnet.
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