Configuration of Aggregation and Core Switches

Core switches provide high-speed Layer 3 routing and redundancy, while aggregation switches consolidate access switch traffic and provide Layer 2/3 services.

Understanding Roles

• Core Switches: Serve as the backbone of the network, handling high-speed packet switching, Layer 3 routing, and connectivity to aggregation switches. They are designed for high throughput, low latency, and fault tolerance .
• Aggregation Switches: Aggregate traffic from multiple access switches, provide Layer 2 and some Layer 3 services, support VLANs, QoS, and link aggregation, and often connect to firewalls or other network services .
• Access Switches: Connect end devices like PCs, IP phones, and APs, often with PoE support, and forward traffic to aggregation switches .

Core Switch Configuration

1. Redundancy and High Availability:
   • Deploy core switches in pairs using technologies like VSX, MC-LAG, or VPC to ensure continuous connectivity .
   • Configure inter-switch links (ISL) using link aggregation (LAG) for the VSX or MC-LAG setup .
2. Routing and Layer 3 Services:
   • Enable dynamic routing protocols such as OSPF or EIGRP for campus or data center connectivity .
   • Configure VLANs for management, transit, and external network routing. Assign SVI interfaces for Layer 3 termination .
3. Management VLAN and Subnet:
   • Set up a management VLAN and assign a gateway IP on the core switch. Enable DHCP for aggregation and access switches if needed .
   • Enable management VLAN auto-negotiation to allow downstream switches to automatically join the management network .

Aggregation Switch Configuration

1. VLAN and Layer 2/3 Setup:
   • Configure VLANs to aggregate access switch traffic. Enable Layer 2 multi-pathing using vPC or LACP for redundancy .
   • Optionally enable Layer 3 routing for inter-VLAN traffic if the aggregation switch supports it .
2. Link Aggregation:
   • Use LACP to bundle multiple physical links between aggregation and core switches for load balancing and failover .
   • For higher resilience, consider MC-LAG to allow two aggregation switches to act as a single logical unit .
3. Integration with Core Switches:
   • Connect aggregation switches to core switches using redundant uplinks.
   • Ensure VLANs and routing configurations match the core switch to maintain seamless traffic flow .

Deployment Best Practices

• Layered Approach: Use a three-tier architecture (core, aggregation, access) for scalability and performance .
• Plug-and-Play Management: For large deployments, import device and Eth-Trunk information into a network controller to enable automatic provisioning .
• Redundancy and Failover: Always configure dual uplinks, LAGs, and VRF/HSRP where applicable to prevent single points of failure .
• Monitoring and Maintenance: Enable LLDP for link discovery and ensure proper monitoring of core and aggregation switches for proactive management . By following these steps, you can configure a robust, scalable, and highly available network where core switches handle routing and aggregation switches efficiently consolidate access traffic.