Support of multi-segment VIM-managed networks

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+# Support of multi-segment VIM-managed networks #
+
+## Proposer ##
+- Gerardo Garcia (Telefonica)
+- Alfonso Tierno (Telefonica)
+- Francisco Javier Ramon (Telefonica)
+
+## Type ##
+**Feature**
+
+## Target MDG/TF ##
+RO
+
+## Description ##
+A VIM, with the help of an SDN controller, can allow the creation of
+multi-segment networks that enables seamless connectivity between legacy VLAN
+domains (e.g. external networks aka provider networks), SR-IOV or Passthrough
+interfaces, and VIRTIO interfaces.
+
+This can be done, for instance, by deploying a VXLAN gateway on the physical
+switches, which must support VXLAN encapsulation and HWVTEP functionality. The
+gateway would be created by the SDN controller, which is controlled by the VIM.
+In the case of Openstack, network configuration is performed using neutron’s
+multi-segment networks and the L2GW service plugin.
+
+This feature will modify the way networks are created in a VIM, assuming that
+the VIM supports multi-segment networks. There are three cases:
+1. Networks where only VIRTIO interfaces are connected
+2. Networks where only dataplane interfaces (SR-IOV or passthrough) are
+connected
+3. Networks where a mix of VIRTIO and dataplane interfaces are connected
+
+In case 1, it is foreseen that the network is created as a single-segment
+network. In cases 2 and 3, it is foreseen that the network will be created as
+multi-segment network. The reason is that VLAN identifiers are a scarce
+resource, while VXLAN Network Identifiers are not. Allocating a VLAN for case 1
+could imply running out of VLANs very quickly, since networks for case 1 are
+typical for cloud application workloads.
+
+In cases 2 and 3, it is foreseen that it would be possible to connect, a
+posteriori, new elements to the already created multi-segment networks.
+
+## Demo or definition of done ##
+To be added.