Overlay Routing

Tenants may have multiple overlays across a data center network where different VLANs belonging to the same tenant are mapped to different VXLAN Network Identifiers (VNIs). Tenants require routing between the VLANs, and VXLAN gateway nodes would need to act as Layer 3 gateways that are capable of routing traffic between tenant VLANs. Inter-overlay routing involves routing:

• Routing traffic from a tenant VLAN into a tunnel with the destination overlay‘s VNI.
• Routing traffic from a tunnel to a tenant VLAN that is different from the tenant VLAN associated with the VNI in the received packet‘s VXLAN header.
• Routing traffic from a tunnel to the same or different tunnel.

A VXLAN tunnel endpoint (VTEP) is designated as the gateway for an overlay by manually configuring it or by running a first hop redundancy protocol (FHRP), such as VRRP on the tenant VLAN on the gateways and letting the protocol determine the placement of the router. ARP is not learned by VXLAN tunnels when the destination MAC address is the VRRP MAC address.