Hi,
Traditional network segmentation has been provided by VLANs that are standardized under the IEEE 802.1Q group. VLANs provide logical segmentation of Layer 2 boundaries or broadcast domains. However, due to the inefficient use of available network links with VLAN use, rigid requirements on device placements in the data center network, and the limited scalability to a maximum 4094 VLANs, using VLANs has become a limiting factor to IT departments and cloud providers as they build large multitenant data centers.
VXLAN (Virtual eXtensible LAN) is a MAC in IP/UDP (MAC-in-UDP) encapsulation technique with a 24-bit segment identifier in the form of a VXLAN ID. The larger VXLAN ID allows LAN segments to scale to 16 million in a cloud network. VXLAN provides a way to extend Layer 2 networks across Layer 3 infrastructure using MAC-in-UDP encapsulation and tunneling.
VXLAN uses VXLAN tunnel endpoint (VTEP) devices to map tenants’ end devices to VXLAN segments and to perform VXLAN encapsulation and de-encapsulation
VXLAN natively operates on a flood-and-learn mechanism where BUM (Broadcast, Unknown Unicast, Multicast) traffic in a given VXLAN network is sent over the IP core to every VTEP that has membership in that network. There are two ways to send such traffic: (1) Using IP multicast (2) Using Ingress Replication or Head-end Replication. Either way, the end hosts and VTEP learning is done through data plane.
One of the biggest limitations of VXLAN flood-and-learn is the actual flooding that is required ensuring that learning happens at the VTEPs. This presents serious scale challenges especially as the number of end hosts go up.
This is addressed via learning using a control-plane for distribution of end host addresses. The control plane of choice is MP-BGP EVPN.
Within BGP, the EVPN address family is employed to carry MAC and IP address information of the end hosts along with other information such as the network and tenant (VRF) to which they belong. This allows optimal forwarding of both layer-2 and layer-3 traffic within the fabric.
In a VXLAN-EVPN based fabric, MAC/IP learning occurs via the control plane (through MP-BGP) instead of the data plane.
In other words, the overlay protocol is VXLAN and BGP uses EVPN as the address family for communicating end host MAC and IP addresses.
Hope it helps,
Sergiu
