Multi-Region Fabric

Multi-Region Fabric

Multi-Region Fabric provides the option to divide the architecture of the Cisco SD-WAN overlay network into the following:

• A core overlay network: this network, called region 0, consists of border routers that connect to regional overlays and connect to each other.

• One or more regional overlay networks: each regional network consists of WAN Edge routers that connect to other WAN Edge routers within the same region and can connect to core region border routers assigned to the region.

The figure shows a core overlay network with six border routers (BR1 to BR6), two assigned to each of the three regions. In the three regional overlay networks, edge routers connect only to other edge routers within the same region or to core border routers assigned to the region.

Multi-Region Fabric creates a distinction between intra-region traffic and inter-region traffic, and these are the differences between them:

• Intra-region traffic: WAN Edge routers connect directly to other WAN Edge routers within the region. Traffic traverses direct tunnels between source devices and destination devices, such as traffic between E1 and E2 WAN Edge routers.

• Inter-region traffic: WAN Edge routers in one region do not connect directly to WAN Edge routers in a different region. For inter-region traffic, the WAN Edge routers connect to the core border routers, which forward the traffic to the core border routers assigned to the target region, and those border routers forward the traffic to the WAN Edge routers within the target region. The traffic traverses three tunnels between the source and destination devices, such as traffic between the E4 and E7 edge routers.

As a network architecture, Multi-Region Fabric adheres to a fundamental tenet whereby various traffic transport services may be deployed across regions and core-region networks once the regions and the core-region network are defined. The core region will typically facilitate traffic transfer between widely separated geographic regions. In such a context, the core region may employ a premium transport service to help ensure optimal performance and cost-effectiveness for long-distance connectivity.

Multi-Region Fabric architecture affords the flexibility to utilize distinct network topologies across various regions. For instance, Region 1 can adopt a complete mesh of Cisco SD-WAN tunnels, Region 2 can implement a hub-and-spoke topology, and Region 3 can utilize a complete mesh topology featuring dynamic tunnels. The best practice is employing a full mesh of tunnels for the overlay topology of the core region (Region 0). This entails that every border router in the core must have a tunnel to each of the other border routers in the core. These direct tunnels ensure optimal connectivity for traffic forwarding between regions. Adhering to a full mesh topology reduces the routing complexity within the core overlay network. In contrast, a partial mesh topology would necessitate topology-aware routing to determine inter-region paths.