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Core Switch Replacement

Replacing a core switch requires careful planning, pre-configuration, staged migration, and a maintenance window to minimize downtime and avoid network disruptions.

Pre-Replacement Preparation

  1. Document the Existing Network: Map all connections, VLANs, SVIs, routing protocols, DHCP/static routes, and upstream/downstream devices such as firewalls and ESXi hosts .
  2. Pre-Configure the New Switch: Apply all configurations offline, including VLANs, SVIs, routing protocols, AAA/TACACS/RADIUS, and IP addresses. Triple-check interface mappings and ensure no IP conflicts with the existing switch .
  3. Test Connectivity: If possible, connect the new switch to a test environment or lab to verify configurations and functionality before the cutover .

Migration Strategies

  1. Staged Migration (Recommended for Minimal Downtime):
    • Bring up the new switch alongside the old one.
    • Shut down one SVI at a time on the old switch and bring it up on the new switch.
    • Move connected devices or VLANs gradually, verifying connectivity after each step.
    • This approach avoids IP conflicts and allows troubleshooting per VLAN or SVI .
  2. All-at-Once Cutover (If Downtime is Acceptable):
    • Schedule a maintenance window.
    • Shut down the old switch completely, move cables to the new switch, and bring it online.
    • This method is simpler but requires planned downtime and a rollback plan in case of issues .

Handling Connected Devices

  • ESXi Hosts: Place hosts in maintenance mode and migrate one host at a time to the new switch. Verify NIC connectivity and storage access before moving additional hosts .
  • Firewalls and Access Switches: Ensure uplinks are ready and pre-tested. If extra ports are available, connect them in a down state until the migration window .
  • Other Critical Devices: Document and pre-configure connections to avoid scrambling during the cutover.

Testing and Verification

  • Verify routing adjacencies, VLAN connectivity, and SVI reachability.
  • Test DHCP, static routes, and any ACLs or firewall rules.
  • Confirm that all critical services and VMs are reachable and functioning.

Rollback Planning

  • Keep the old switch powered and ready to reconnect if the new switch fails.
  • Document all steps and maintain a checklist for quick recovery.

Best Practices

  • Perform a dry run in a lab or off-hours to estimate downtime.
  • Communicate the maintenance window to all stakeholders.
  • Ensure all firmware and software versions are compatible.
  • Maintain detailed documentation for post-migration review . By following these steps, you can replace a core switch efficiently while minimizing downtime and reducing the risk of network disruption.

Core Switch Replacement - Kili Optical & Telecom Technologies [PDF]

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