Cisco Nexus 7000 Series Configuration Manual page 49

Configuring VXLAN BGP EVPN
ToR2 decapsulates the VXLAN packet addressed to it. It does a lookup on the inner frame. Through its end
host database, ToR2 recognizes that VM B is attached to it and belongs to segment x, forwards the original
frame to VM B.
Figure 4: VXLAN Overlay
• VXLAN semantics are in operation from ToR1 to ToR2 through the encapsulation and decapsulation
at source and destination VTEPs, respectively. The overlay operation ensures that the original frame/packet
content is not exposed to the underlying IP network.
• The IP network that sends packets from ToR1 to ToR 2 based on the outer packet source and destination
address forms the underlay operation. As per design, none of the spine switches need to learn the addresses
of end hosts below the ToRs. So, learning of hundreds of thousands of end host IP addresses by the
spine switches is avoided.
Learning of (hundreds of thousands of) end host IP and MAC addresses
One of the biggest limitations of VXLAN flood and learn is the inherent flooding that is required ensuring
that learning happens at the VTEPs. In a traditional deployment, a layer-2 segment is represented with a VLAN
that comprises a broadcast domain, which also scopes BU traffic. With VXLAN, now the layer-2 segment
spans a much larger boundary across an IP core where floods are translated to IP multicast (or HER).
Consequently, the flood-n-learn based scheme 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. By implementing MP-BGP EVPN with VXLAN, the following
is made possible:
• End hosts' information is available to the attached ToR via First Hop Protocols such as ARP/ND/DHCP
etc., when a new bare-metal server or VM is attached.
Introducing IP Fabric Overlays (VXLAN)
Cisco Nexus 7000 Series NX-OS VXLAN Configuration Guide
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