Site-to-Site (S2S) VPN Security Checklist

1. Identity and Access Management

1. Use Microsoft Entra ID for administrative access control
2. Enforce Role-Based Access Control with least privilege
3. Avoid broad roles such as Owner or Contributor
4. Use Privileged Identity Management for network administrators
5. Enforce Multi-Factor Authentication for all privileged users
6. Regularly review and remove unused access

2. VPN Gateway Security

1. Use Azure VPN Gateway with latest supported SKU
2. Keep gateway configurations up to date
3. Restrict management access to trusted administrators only
4. Monitor gateway health and performance
5. Use active-active configuration for high availability

3. Encryption and Protocol Security

1. Use strong encryption standards such as AES256
2. Use IKEv2 instead of IKEv1 where possible
3. Configure secure IPsec policies
4. Avoid weak cryptographic algorithms
5. Ensure Perfect Forward Secrecy is enabled
6. Regularly review and update encryption settings

4. Authentication and Key Management

1. Use certificate-based authentication where possible
2. Avoid weak pre-shared keys
3. Rotate pre-shared keys regularly
4. Store secrets securely (Key Vault recommended)
5. Limit access to keys and certificates
6. Monitor authentication attempts

5. Network Segmentation and Access Control

1. Restrict traffic between on-premises and Azure networks
2. Use NSGs to control inbound and outbound traffic
3. Implement least privilege network access rules
4. Segment networks based on workload and trust level
5. Avoid full network exposure across the tunnel
6. Use route tables to control traffic flow

6. Routing and Traffic Control

1. Validate route configurations carefully
2. Use BGP securely and validate route advertisements
3. Avoid unnecessary route propagation
4. Prevent asymmetric routing
5. Monitor routing changes
6. Document routing design

7. Monitoring and Logging

1. Enable diagnostic logging for VPN Gateway
2. Send logs to Log Analytics or SIEM
3. Monitor connection status and uptime
4. Track failed connection attempts
5. Set alerts for anomalies
6. Review logs regularly

8. Threat Protection

1. Monitor for unusual traffic patterns
2. Detect potential lateral movement across networks
3. Use Microsoft Defender for Cloud for visibility
4. Investigate anomalies promptly
5. Protect against unauthorized access attempts

9. Hybrid Environment Security

1. Secure on-premises VPN devices
2. Keep firmware and software updated
3. Restrict access to on-prem VPN endpoints
4. Use firewalls to control hybrid traffic
5. Validate both sides of the tunnel for compliance

10. High Availability and Resilience

1. Use active-active VPN gateways
2. Deploy redundant on-prem VPN devices
3. Configure multiple tunnels where possible
4. Test failover scenarios regularly
5. Monitor uptime and performance

11. Governance and Compliance

1. Use Azure Policy to enforce VPN configurations
2. Standardize VPN deployment configurations
3. Document architecture and security settings
4. Implement change management processes
5. Regularly review compliance requirements

12. Backup and Recovery

1. Document VPN configurations
2. Backup configuration settings
3. Maintain recovery procedures
4. Test restoration processes
5. Ensure quick recovery from failures

13. Continuous Security Operations

1. Perform regular VPN security assessments
2. Audit configurations periodically
3. Continuously monitor VPN activity
4. Update configurations based on threats
5. Validate security posture regularly
6. Maintain documentation

Always use best practices. Never assume trust. Always verify access. Security is not static and must be continuously monitored, reviewed, and improved.