Lessons Learned

This document collects practical findings from the physical Cisco lab.

IOS Maintenance

• A successful transfer does not prove image integrity; verify size and checksum.
• Define the fallback boot image before reloading.
• Keep serial console access available for disruptive maintenance.
• Observe image validation, bootloader changes, POST and interface recovery during boot.
• Remove temporary services and client-side compatibility exceptions after the maintenance window.

SSH and SCP

• A modern OpenSSH client may require legacy compatibility settings when connecting to an older IOS release.
• After upgrading IOS, direct SSH should be retested before retaining those exceptions.
• Classic SCP mode may still be required with scp -O because the switch does not provide an SFTP subsystem.
• SSH and SCP compatibility are related but not identical checks.

Credentials

• Legacy Type 5 secrets should be replaced when the platform supports stronger Type 9 storage.
• Never publish password hashes, even when they appear encrypted.
• Test the new login and privileged access in a separate session before closing the working session.

NTP and DNS

• A hostname-based NTP server is unsuitable when DNS lookup is deliberately disabled and no resolver path is configured.
• A local router acting as NTP source gives the lab a simple, low-latency time hierarchy.
• Timezone and daylight-saving configuration remain necessary even after NTP synchronization.
• Accurate timestamps materially improve log correlation and troubleshooting.

Topology and Risk Separation

• A wireless repeater operating as a bridge extends the same Layer 2 home LAN; it does not create a routed lab network.
• A future Cisco router should initially sit behind the existing home router and serve an isolated lab subnet.
• This limits DHCP, NAT, ACL, routing and IPv6 mistakes to the lab.
• STP loops and redundant links should be created only on dedicated lab ports.

Portfolio Documentation

• Document verified outcomes rather than presenting planned hardware as already implemented.
• Keep the switching repository focused on device operation and Cisco CLI work.
• Keep data collection, Python, SQL, data quality and BI outputs in the related network-operations-data-lab.
• Publish sanitized methods and architecture, not the real home topology or raw configuration.