How to modify the core switch

To modify or replace a core switch safely, prepare the new switch configuration in advance, plan cable migration, and execute changes during a maintenance window to minimize downtime.PreparationPre-configure the new switch: Build the configuration on the new switch ahead of time, including VLANs, SVIs, routing protocols, HSRP/VRRP, AAA, and management IPs. Verify that all interface mappings match the existing core switch .Check IP addresses: Avoid conflicts by ensuring the new switch does not go live with the same IPs as the old switch until the migration is ready .Document the network: Map all connections, including uplinks to firewalls, routers, and edge switches. Identify which ports carry critical traffic and which can be migrated gradually .Migration StrategiesDirect swap during maintenance window:Shut down the old switch.Connect the new switch and move all cables.Activate SVIs and routing protocols on the new switch.This method is simple but requires planned downtime .Gradual migration with minimal downtime:Connect the new switch to the old one using trunk links.Configure SVIs and routing on the new switch in shutdown mode.Move VLANs or ports one at a time: shut down the VLAN on the old switch, bring it up on the new switch, and migrate cables gradually .This reduces downtime but requires careful IP and routing management to avoid conflicts .Use extra cabling for rollback:Keep existing cables on the old switch and use new cables for the new switch.If issues occur, revert quickly without re-cabling .Configuration and TestingVerify connectivity: Test SVIs, routing adjacencies, and ping between switches before moving production traffic .Check redundancy: If using HSRP, VRRP, or vPC, ensure the new switch is ready to take over without disrupting failover .Port security and ACLs: Apply port security and ACLs as per the old switch configuration to maintain network policies .Post-MigrationMonitor traffic and logs for anomalies.Confirm all VLANs, routing, and management access are functioning.Document the new switch configuration and update network diagrams . By following these steps, you can replace or modify a core switch efficiently while minimizing downtime and avoiding IP conflicts, ensuring a smooth transition for your network.