The traditional 3-tier design is based on a Layer 2 fabric, as shown in the following figure:
Figure 36. Traditional 3-Tier Layer 2 Fabric Design
It has the following characteristics:
- VLANs carried throughout the fabric –increases the size of the broadcast domain beyond racks if multiple racks are needed for the infrastructure and clusters span racks.
- The aggregation layer devices of each pod are the demarcation line between L2 and L3 network domains.
- Default Gateway – HSRP/VRRP at the aggregation layer
- The NSX-T T0 Gateway peers with the routers at the aggregation layer.
- VLANs can span racks which can be useful for VxRail system VLANs like vSAN/vMotion and node discovery.
- Layer 2 design might be considered less complex to implement.
- Large clusters spanning racks will create large broadcast domains.
- Interoperability issues between different switch vendors can introduce spanning tree issues in large fabrics.
- The NSX-T T0 gateways for each WLD needs to peer at the aggregation layer. For large-scale deployments with multiple WLDs, the configuration becomes complex.
- The size of such a deployment is limited because the fabric elements have to share a limited number of VLANs 4094. With NSX, the number of VLANs could be reduced so this might not be an issue.