====== SDN ======

Software Defined Network

  * **Zone** - upper level:
    * VMs are assigned to zones.
    * user permissions are applied to zones
    * zones are containers of ''VNets''
    * zone types:
      * **Simple** a simple bridge on single Proxmox node - no communication across the cluster.
        * usage: user friendly zone names instead of ''vmbrX'' interfaces. But still needs to specify VLAN tag for VLANs.
      * **VLAN** 
        * like above but with VLAN tag assigned
      * **QinQ** - 802.1Q tunnelling / stacked VLANs / 802.1ad
        * first VLAN tag in L2 frame is a provider / service vlan 
        * 2nd VLAN tag in L2 frame is customer tag
      * **VxLAN** RFC 7348 (tech preview) 
        * encapsulate L2 frames in L3 UDP packets.
        * L3 networks solves lots of forwarding/routing problems of L2 networks. No STP nor VLANs needed.
        * well known protocols like OSPF, EIGRP can be used for L3.
        * VNI tag is 24 bit (16 777 215 VxLANs)
        * one VxLAN is a group of Virtual Tunnels. VTEPs (Virtual Tunnel Endpoint) acts like switch
      * **EVPN** (tech preview)
  * **VNets** - lower