I monitor VPC performance using VPC Flow Logs, CloudWatch metrics, Reachability Analyzer, and Route 53 Resolver logs. I track packet drops, throughput, latency, DNS performance, VPN tunnel health, and rejected traffic. I also create CloudWatch alarms for abnormal network behavior and use Traffic Mirroring or Network Insights for advanced troubleshooting. Together, these tools provide visibility into both network performance and connectivity issues.