Cisco Nexus 7000 Series Configuration Manual page 128

Layer 2 Multicast Forwarding and Layer 3 Multicast Routing
traffic and sends bridged traffic to relevant Layer 2 switches (or receivers in the Layer 2 CE pod). For
receivers in DC-2, DC-3, or DC-4, the border leaf switch VXLAN decapsulates the traffic and sends
traffic over OTV to DC-2, DC-3 (or DC-4).
• When the DC-2 border leaf switch receives the packets, it has to send traffic to receivers in the VXLAN
fabric and in the Layer 2 CE pod. For receivers within the VXLAN fabric, the border leaf switch OTV
decapsulates the traffic, VXLAN encapsulates it, and sends it towards relevant ToR/leaf switches. For
receivers in the CE pod, the traffic is OTV decapsulated and sent towards relevant Layer 2 CE switches.
• When a DC-3 OTV switch receives the packets, the switch OTV decapsulates the traffic and sends a
copy of the bridged traffic towards relevant Layer 2 CE switches/receivers.
• When the designated DC-4 OTV+BDI border vPC switch receives the packets, it OTV decapsulates the
traffic and sends a copy of the bridged traffic towards relevant Layer 2 CE switches/receivers.
• Similarly, when a server in the Layer 2 CE pod (in DC-1 or DC-2) sends multicast traffic, traffic flow
to receivers within the CE pod remains the same. If there are receivers in the VXLAN fabric in DC-1,
and in DC-2 and DC-3, the attached access switch sends it towards the border leaf switch. The border
leaf switch sends traffic to receivers in the VXLAN fabric (in DC-1), and towards DC-2 and DC-3, as
explained in the previous points. If there are receivers in DC-4 (per topology 2), a copy of the packets
is sent towards DC-4.
• When a server in DC-4 (OTV+BDI one box solution at the border) sends Layer 2 multicast traffic, traffic
flow to receivers within the CE pod remains the same. If there are receivers in other datacenters, the
switch at the datacenter border receives the packets, and sends it over OTV towards the destination
datacenters (DC-1 and DC-3). If DC-4 has multicast receivers and receives multicast traffic from a
sender in another datacenter, it OTV decapsulates the traffic and sends a copy of the bridged traffic
towards relevant Layer 2 CE switches/receivers. The Layer 2 switch(es) forwards the packets to intended
destination servers.
Layer 3 multicast routing
When a server in DC-1 or DC-2 (in topology 1), or DC-1/DC-4 (in topology 2) sends Layer 3 multicast traffic
across the fabrics, it is routed through the external, centralized multicast gateway in the legacy datacenter,
DC-3. Layer 3 multicast routing support is not available for the VXLAN BGP EVPN and OTV Interoperation
feature in release 8.2(1). On the border leaf switch, ensure that you do not enable the ip pim sparse-mode
command on OTV enabled bridge domains.
Attention Layer 3 multicast traffic within a VXLAN BGP EVPN fabric (for VXLAN enabled bridge domains) is
supported as usual. This is the use case wherein a sender within the VXLAN fabric sends Layer 3 multicast
traffic to receivers located within the fabric. For more details, see "Multicast Routing in the VXLAN
Underlay" section, "IP Fabric Underlay" chapter in the Cisco Programmable Fabric with VXLAN BGP
EVPN Configuration Guide.
Layer 3 multicast packet flow in DC-1 and DC-2:
• If a server in the VXLAN fabric in DC-1 sends multicast traffic to receivers in different VLANs/subnets
outside the VXLAN fabric, then the traffic is sent to the Layer 3 switch in DC-3 where the centralized
multicast gateway is enabled. First, the traffic reaches the border leaf switch in DC-1. Assuming that a
receiver is located in the CE pod in DC-1 and another receiver in the VXLAN fabric in DC-2, the border
leaf switch forwards the traffic towards DC-3. On receiving the request, the Layer 3 switch (or centralized
multicast gateway) in DC-3 sends a copy of the routed multicast traffic to the border leaf switch in DC-1
and DC-2. On receiving the traffic, the border leaf switch in DC-2 VXLAN encapsulates the traffic and
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VXLAN BGP EVPN and OTV Interoperation