How to connect the aggregation switch to the core switch

Connect aggregation switches to core switches using redundant uplinks with link aggregation and proper VLAN configuration to ensure high availability and efficient traffic flow.

Physical Connection

1. Redundant Uplinks: Use at least two uplink ports from the aggregation switch to the core switch to provide redundancy and load balancing .
2. Fiber or High-Speed Links: Typically, 10GbE or higher connections are used between aggregation and core switches to handle aggregated traffic from multiple access switches .
3. Port Mapping: Ensure you know which ports on the core switch correspond to the aggregation switch uplinks. Commands like display device wdm-port mapping slot (Huawei) or equivalent on Cisco/Aruba can help identify ports .

Logical Configuration

1. Link Aggregation: Configure the uplinks as a Port-Channel (Cisco) or Eth-Trunk (Huawei) to combine multiple physical links into a single logical link. This increases bandwidth and provides failover in case one link fails .
   • For Layer 2 aggregation, LACP (Link Aggregation Control Protocol) is recommended.
   • For static aggregation, manual configuration of active/standby links is possible.
2. VLAN Configuration: Allow the required VLANs (management and service VLANs) to pass through the uplinks. Use VLAN transparent transmission if needed to ensure all necessary traffic reaches the core .
3. Redundancy and High Availability:
   • Configure active/standby mode for Eth-Trunks or Port-Channels to prevent loops and ensure failover .
   • If using VSX, VSS, or MC-LAG, connect uplinks from different stack members to separate aggregation switches for fault tolerance .

Best Practices

• Oversubscription Ratio: Maintain a 4:1 or appropriate oversubscription ratio between core and aggregation layers to prevent congestion .
• Layer 2 vs Layer 3: Aggregation switches can operate at Layer 2 initially, but consider enabling Layer 3 in the future for routing and redundancy .
• Monitoring and Testing: After configuration, verify link status, VLAN propagation, and failover behavior to ensure reliable connectivity. By following these steps, the aggregation switch will efficiently consolidate traffic from access switches and forward it to the core switch with redundancy, high availability, and proper VLAN handling, ensuring a scalable and resilient network architecture .