Connecting two core switches

The optimal way to connect two core switches is to use a combination of Layer-3 point-to-point links for routing and Layer-2 trunks for VLAN traffic, ensuring redundancy and proper spanning tree configuration.Connection Methods1. Layer-3 Point-to-Point Links: For core switches, it is recommended to establish Layer-3 connections using dedicated VLAN interfaces (SVIs) or routed ports. Each link should have its own subnet and IP addresses, allowing the switches to route traffic efficiently without creating Layer-2 loops. This approach reduces STP complexity and avoids broadcast storms between cores (Cisco community guidance) . 2. Layer-2 Trunks: In addition to Layer-3 links, a Layer-2 trunk can be configured between the core switches to carry multiple VLANs. This trunk allows VLAN traffic to traverse both switches while maintaining VLAN separation. It is common to create a dedicated VLAN for the point-to-point link to simplify management and avoid conflicts with production VLANs . 3. Redundancy and Spanning Tree:Use Rapid-PVST or MSTP to manage Layer-2 loops.Define primary and secondary root bridges for each VLAN to control traffic paths.Align HSRP or VRRP active gateways with the spanning tree topology to ensure optimal routing for end devices . 4. Stacking vs Cascading:Stacking: If the switches support stacking, use stacking ports and cables to create a single logical switch. This provides high bandwidth and simplified management but requires switches from the same vendor .Cascading: If stacking is not supported, connect switches using multiple Ethernet links (port channels) to increase bandwidth and provide redundancy. Each switch remains independently managed .Best PracticesUse link aggregation (LACP) for multiple physical connections to increase throughput and provide failover.Separate management VLANs from data VLANs to improve security and monitoring.Ensure consistent firmware and configuration across core switches to prevent compatibility issues.Monitor traffic and STP states to detect potential bottlenecks or misconfigurations early. By combining Layer-3 routing for core connectivity with Layer-2 trunks for VLAN traffic, and implementing redundancy and proper STP/HSRP alignment, you can achieve a resilient, high-performance core network that minimizes downtime and maximizes bandwidth utilization .