Interconnection between 2 core switches

Core switches are typically interconnected using multiple high-speed links with VLAN trunking and static or dynamic routing to ensure redundancy and high availability.

Key Considerations

1. Physical Connectivity: Use fiber optic links for long-distance or high-bandwidth connections between core switches. Single-mode fiber is preferred for distances over a few hundred meters, while multi-mode fiber works for shorter distances. Pre-terminated fiber cables with LC or SC connectors simplify installation and reduce errors . For redundancy, deploy at least two physical links, ideally across different linecards or port groups to avoid a single point of failure . 2. VLAN and Trunk Configuration: Create a transport VLAN dedicated to inter-switch communication. Assign IP addresses to the VLAN interfaces on each switch for routing purposes. Configure the interconnect ports as trunk ports and allow the transport VLAN along with any other VLANs that need to traverse the link. Ensure that VLAN IDs are unique and consistent across both switches to prevent MAC address conflicts . 3. Routing Between Switches: If each core switch manages its own VLANs, use static routes or a dynamic routing protocol (e.g., OSPF or EIGRP) over the transport VLAN to enable inter-VLAN communication. For example, on CS1, you might configure ip route 12.0.0.0 255.255.255.0 10.0.0.2 pointing to CS2's transport VLAN IP . Verify connectivity with ping tests and check MAC address tables to ensure proper forwarding. 4. Redundancy and Bandwidth Aggregation: Consider link aggregation (LACP) to combine multiple physical links into a single logical interface, increasing bandwidth and providing failover. Avoid single-link interconnects, as they create a bottleneck and a single point of failure . 5. Topology Choices:

• Cascading: Simple method connecting two switches via trunk ports; each switch remains independently managed .
• Stacking: If supported, allows switches to operate as a single logical unit with shared management and backplane bandwidth, but usually requires same-vendor hardware .
• Daisy Chain or Star Topology: For multiple switches, daisy chain is simple but less redundant; star topology centralizes traffic through a main switch, improving performance and manageability . 6. Verification and Troubleshooting:
• Use show cdp neighbor to confirm the switches see each other.
• Use show vlan and show interface trunk to verify VLANs are active and not pruned.
• Check MAC addresses to ensure no conflicts exist on the transport VLAN . By following these practices, you can interconnect two core switches efficiently, ensuring high availability, proper routing, and scalable bandwidth for your network.