VLAN partitioning via aggregation switch

VLAN partitioning in core and aggregation layers uses sub-VLANs aggregated into super-VLANs to optimize broadcast domains, IP usage, and traffic flow across hierarchical networks.Core and Aggregation Switch RolesCore switches act as the high-speed backbone, connecting distribution/aggregation switches and handling large traffic volumes with low latency and high reliability. They primarily operate at Layer 3, providing routing between VLANs and inter-subnet communication, and often support advanced redundancy and ECMP for deterministic convergence . Aggregation (distribution) switches sit between access and core layers. They aggregate traffic from multiple access switches, enforce policies like QoS and ACLs, and may provide Layer 2 and Layer 3 services. Aggregation switches often implement link aggregation and VLAN management to efficiently transport traffic to the core .VLAN Aggregation ConceptsVLAN aggregation, also called super-VLAN, allows multiple sub-VLANs to share a single Layer 3 interface and subnet. Key points include :Super-VLAN: A logical Layer 3 construct that contains multiple sub-VLANs. Only the Layer 3 interface exists; physical ports are not directly assigned. It provides a shared default gateway for all sub-VLANs.Sub-VLAN: Contains physical ports and isolates broadcast domains. Sub-VLANs do not require independent Layer 3 interfaces and can share the super-VLAN's IP subnet.Benefits: Reduces the number of required IP addresses, allows multiple broadcast domains to coexist in the same subnet, and simplifies Layer 3 routing. For example, a super-VLAN can include several sub-VLANs, each representing a different access switch or group of hosts. All sub-VLANs share the same subnet and default gateway, while maintaining separate broadcast domains. This approach optimizes IP address usage and reduces the overhead of creating multiple Layer 3 interfaces .Deployment StrategyAccess Layer: Connect end devices to access switches, assign them to sub-VLANs.Aggregation Layer: Aggregate sub-VLAN traffic into super-VLANs, enforce policies, and provide redundancy using MC-LAG or VPC.Core Layer: Route between super-VLANs, provide high-speed interconnects, and maintain fault tolerance with redundant links and ECMP routing . Best Practices:Use super-VLANs to reduce IP wastage and simplify Layer 3 management.Maintain redundant links between aggregation and core switches for high availability.Implement Layer 3 routing at the core to isolate broadcast traffic and optimize performance.Consider a 20:1 oversubscription ratio between aggregation and access layers for typical campus networks . By combining VLAN aggregation with hierarchical switch design, networks achieve scalability, efficient IP utilization, and fault-tolerant traffic management.