Firewalls - Security group rule design least privilege access troubleshooting blocked traffic, VPN - Site-to-site VPN IKE IPsec configuration tunnel troubleshooting SNAT NAT over VPN, Routing - Static routing BGP basics route table design asymmetric routing diagnosis, AWS Networking - VPC subnets route tables security groups NACLs VGW CGW, DNS - Route 53 DNS record types TTL management resolution troubleshooting, Network Troubleshooting - tcpdump Wireshark traceroute connectivity debugging, Monitoring - Tools like DataDog Solar Winds Prometheus PRTG