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+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+.. (c) Bin Hu
+
+L3VPNs are virtual layer 3 networks described in multiple standards and RFCs,
+such as [RFC4364]_ and [RFC7432]_. Connectivity as well as traffic separation is
+achieved by exchanging routes between VRFs (Virtual Routing and Forwarding).
+
+Moreover, a Service Providers' virtualized network infrastructure may consist of
+one or more SDN Controllers from different vendors. Those SDN Controllers may be
+managed within one cloud or multiple clouds. Jointly, those VIMs (e.g. OpenStack
+instances) and SDN Controllers work together in an interoperable framework to
+create L3 services in the Service Providers' virtualized network infrastructure.
+
+While interoperability between SDN controllers and the corresponding data planes
+is ensured based on standardized protocols (e.g., [RFC4364]_ and [RFC7432]_),
+the integration and management of different SDN domains from the VIM is not
+clearly defined. Hence, this section analyses three L3VPN use cases involving
+multiple SDN Controllers.
+
+
+
+Any-to-Any Base Case
+--------------------
+
+Description
+~~~~~~~~~~~
+
+This any-to-any use case is the base scenario, providing layer 3 connectivity
+between VNFs in the same L3VPN while separating the traffic and IP address
+spaces of different L3VPNs belonging to different tenants.
+
+There are 2 hosts (compute nodes). SDN Controller A and vForwarder A are
+provided by Vendor A and run on host A. SDN Controller B and vForwarder B
+are provided by Vendor B, and run on host B.
+
+There are 2 tenants. Tenant 1 creates L3VPN Blue with 2 subnets: 10.1.1.0/24 and
+10.3.7.0/24.  Tenant 2 creates L3VPN Red with 1 subnet and an overlapping
+address space: 10.1.1.0/24. The network topology is shown in
+:numref:`l3vpn-any2any-figure`.
+
+.. figure:: images/l3vpn-any2any.png
+   :name:  l3vpn-any2any-figure
+   :width: 100%
+
+In L3VPN Blue, VMs G1 (10.1.1.5) and G2 (10.3.7.9) are spawned on host A, and
+attached to 2 subnets (10.1.1.0/24 and 10.3.7.0/24) and assigned IP addresses
+respectively. VMs G3 (10.1.1.6) and G4 (10.3.7.10) are spawned on host B, and
+attached to 2 subnets (10.1.1.0/24 and 10.3.7.0/24) and assigned IP addresses
+respectively.
+
+In L3VPN Red, VM G5 (10.1.1.5) is spawned on host A, and attached to subnet
+10.1.1.0/24. VM G6 (10.1.1.6) is spawned on host B, and attached to the same
+subnet 10.1.1.0/24.
+
+
+
+Derived Requirements
+~~~~~~~~~~~~~~~~~~~~~
+
+Northbound API / Workflow
++++++++++++++++++++++++++
+
+.. **Georg: this section needs to be made more readable**
+
+An example of the desired workflow is as follows:
+
+1. Create Network
+
+2. Create Network VRF Policy Resource ``Any-to-Any``
+
+  2.1. This policy causes the following configuration when a VM of this tenant is spawned on a host:
+
+    2.1.1. There will be a RD assigned per VRF
+
+    2.1.2. There will be a RT used for the common any-to-any communication
+
+3. Create Subnet
+
+4. Create Port (subnet, network VRF policy resource). This causes the controller to:
+
+  4.1. Create a VRF in vForwarder's FIB, or update VRF if it already exists
+
+  4.2. Install an entry for the guest's host route in FIBs of the vForwarder serving this tenant's virtual network
+
+  4.3. Announce guest host route to WAN-GW via MP-BGP
+
+
+
+
+Current implementation
+~~~~~~~~~~~~~~~~~~~~~~
+
+Support for creating and managing L3VPNs is available in OpenStack Neutron by
+means of the [BGPVPN]_ project. In order to create the L3VPN network
+configuration described above using the API [BGPVPN]_ API, the following workflow
+is needed:
+
+1. Create Neutron networks for tenant "Blue"
+
+  ``neutron net-create --tenant-id Blue net1``
+
+  ``neutron net-create --tenant-id Blue net2``
+
+
+2. Create subnets for the Neutron networks for tenant "Blue"
+
+  ``neutron subnet-create --tenant-id Blue --name subnet1 net1 10.1.1.0/24``
+
+  ``neutron subnet-create --tenant-id Blue --name subnet2 net2 10.3.7.0/24``
+
+
+3. Create Neutron ports in the corresponding networks for tenant "Blue"
+
+   ``neutron port-create --tenant-id Blue --name G1 --fixed-ip subnet_id=subnet1,ip_address=10.1.1.5 net1``
+
+   ``neutron port-create --tenant-id Blue --name G2 --fixed-ip subnet_id=subnet1,ip_address=10.1.1.6 net1``
+
+   ``neutron port-create --tenant-id Blue --name G3 --fixed-ip subnet_id=subnet2,ip_address=10.3.7.9 net2``
+
+   ``neutron port-create --tenant-id Blue --name G4 --fixed-ip subnet_id=subnet2,ip_address=10.3.7.10 net2``
+
+
+4. Create Neutron network for tenant "Red"
+
+  ``neutron net-create --tenant-id Red net3``
+
+
+5. Create subnet for the Neutron network of tenant "Red"
+
+  ``neutron subnet-create --tenant-id Red --name subnet3 net3 10.1.1.0/24``
+
+
+6. Create Neutron ports in the networks of tenant "Red"
+
+  ``neutron port-create --tenant-id Red --name G5 --fixed-ip subnet_id=subnet3,ip_address=10.1.1.5 net3``
+
+  ``neutron port-create --tenant-id Red --name G7 --fixed-ip subnet_id=subnet3,ip_address=10.1.1.6 net3``
+
+
+7. Create a L3VPN by means of the BGPVPN API for tenant "Blue"
+
+  ``neutron bgpvpn-create --tenant-id Blue --route-targets AS:100 --name vpn1``
+
+
+8. Associate the L3VPN of tenant "Blue" with the previously created networks
+
+  ``neutron bgpvpn-net-assoc-create --tenant-id Blue --network net1 --name vpn1``
+
+  ``neutron bgpvpn-net-assoc-create --tenant-id Blue --network net2 --name vpn1``
+
+
+9. Create a L3VPN by means of the BGPVPN API for tenant "Red"
+
+  ``neutron bgpvpn-create --tenant-id Red --route-targets AS:200 --name vpn2``
+
+
+10. Associate the L3VPN of tenant "Red" with the previously created networks
+
+  ``neutron bgpvpn-net-assoc-create --tenant-id Red --network net3 --name vpn2``
+
+
+Comments:
+
+* In this configuration only one BGPVPN for each tenant is created.
+
+* The ports are associated indirectly to the VPN through their networks.
+
+* The BGPVPN backend takes care of distributing the /32 routes to the vForwarder
+  instances and assigning appropriate RD values.
+
+
+
+Gaps in the current solution
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In terms of the functionality provided by the BGPVPN project, there are no gaps
+preventing this particular use case from a L3VPN perspective.
+
+However, in order to support the multi-vendor aspects of this use case, a better
+support for integrating multiple backends is needed (see previous use case).
+
+