Considerations For The Transport Network - Cisco Nexus 9000 Series Configuration Manual

Guidelines and Limitations for VXLAN BGP EVPN
segments causes a parallel increase in the required multicast address space and the amount of forwarding
states on the core network devices. At some point, multicast scalability in the transport network can
become a concern. In this case, mapping multiple VXLAN segments to a single multicast group can
help conserve multicast control plane resources on the core devices and achieve the desired VXLAN
scalability. However, this mapping comes at the cost of suboptimal multicast forwarding. Packets
forwarded to the multicast group for one tenant are now sent to the VTEPs of other tenants that are
sharing the same multicast group. This causes inefficient utilization of multicast data plane resources.
Therefore, this solution is a trade-off between control plane scalability and data plane efficiency.
Despite the suboptimal multicast replication and forwarding, having multiple-tenant VXLAN networks
to share a multicast group does not bring any implications to the Layer 2 isolation between the tenant
networks. After receiving an encapsulated packet from the multicast group, a VTEP checks and validates
the VNID in the VXLAN header of the packet. The VTEP discards the packet if the VNID is unknown
to it. Only when the VNID matches one of the VTEP's local VXLAN VNIDs, does it forward the packet
to that VXLAN segment. Other tenant networks will not receive the packet. Thus, the segregation
between VXLAN segments is not compromised.

Considerations for the Transport Network

The following are considerations for the configuration of the transport network:
• On the VTEP device:
• Throughout the transport network:
• When using SVI uplinks with VXLAN enabled on Cisco Nexus 9200 Series switches and Cisco Nexus
9300-EX switches, use the system nve infra-vlans command to specify the VLANs that are used for
uplink SVI. Failing to specify the VLANs results in traffic loss.
Note * Not required for static ingress replication or BGP EVPN ingress replication.
Cisco Nexus 9000 Series NX-OS VXLAN Configuration Guide, Release 7.x
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◦ Enable and configure IP multicast.*
◦ Create and configure a loopback interface with a /32 IP address.
(For vPC VTEPs, you must configure primary and secondary /32 IP addresses.)
◦ Enable IP multicast on the loopback interface.*
◦ Advertise the loopback interface /32 addresses through the routing protocol (static route) that runs
in the transport network.
◦ Enable IP multicast on the uplink outgoing physical interface.*
◦ Enable and configure IP multicast.*
Configuring VXLAN BGP EVPN