Setting Up Active/Active or Active/Passive AWS Direct Connect Configuration

Introduction

AWS Direct Connect provides dedicated network connectivity between on-premises environments and AWS, offering better performance and security compared to standard internet-based VPNs. When designing a Direct Connect network, companies must choose between an Active/Active or Active/Passive configuration based on cost, resiliency, and traffic management needs.

• Active/Active: Maximizes bandwidth and resiliency by utilizing both links simultaneously. However, it can incur higher data transfer costs due to increased utilization.
• Active/Passive: More cost-effective, as only one link is primarily used, reducing overall bandwidth costs. The secondary link serves as a backup in case of failure.

This guide explores both configurations using a real-world scenario, covering failover mechanisms, load balancing, BGP community tagging, AS Path Prepending, and monitoring strategies.

Use Case Scenario

A company has two AWS Direct Connect connections in different AWS Regions:

• On-premises Data Center 1 (DC1) in us-east-1.
• On-premises Data Center 2 (DC2) in us-west-2.
• Two private VIFs: VIF A in us-east-1 (DC1) and VIF B in us-west-2 (DC2).
• Inter-data center connection exists between DC1 and DC2.
• Direct Connect gateway is used to connect to two VPCs.
• Traffic separation: Production prefers VIF A and Development prefers VIF B.
• BGP Community Tags Used: Production traffic: VIF A: 7224:7300 (High Preference) and VIF B: 7224:7100 (Low Preference) Development traffic: VIF B: 7224:7300 (High Preference) VIF A: 7224:7100 (Low Preference)

Why These BGP Community Tags?

• 7224 is AWS’s Autonomous System Number (ASN).
• 7300 (High Preference) and 7100 (Low Preference) are customer-defined values that AWS uses to prioritize routes.
• The higher preference tag (7300) ensures the preferred VIF is selected unless a failure occurs.

Configuring Active/Passive Direct Connect Setup

An Active/Passive setup ensures that one Direct Connect link is preferred for a specific type of traffic while the other serves as a backup. If the primary link fails, the secondary takes over.

Step 1: Configure the Direct Connect Gateway

1. Create a Direct Connect Gateway in AWS.
2. Associate it with the private VIFs (VIF A in us-east-1 and VIF B in us-west-2).
3. Attach the Direct Connect Gateway to the VPCs that require connectivity.

Step 2: Configure BGP Sessions on the On-Premises Routers

For Production Traffic:

• VIF A (Primary for Production) → High preference

Apply BGP Community Tag: 7224:7300        

• VIF B (Backup for Production) → Low preference

Apply BGP Community Tag: 7224:7100        

For Development Traffic:

• VIF B (Primary for Development) → High preference

Apply BGP Community Tag: 7224:7300        

• VIF A (Backup for Development) → Low preference

Apply BGP Community Tag: 7224:7100
        

These tags ensure production traffic always prefers VIF A, while development traffic prefers VIF B. If a Direct Connect link fails, the backup path takes over.

Step 3: Failover Mechanism

• BFD (Bidirectional Forwarding Detection) a low-overhead, short-duration protocol can be enabled to speed up detection of link failures, reducing failover time to sub-second levels.
• Without BFD, failover relies on BGP keepalive timers, which can introduce brief interruptions (typically 30–90 seconds).
• For example we can enable Bidirectional Forwarding Detection (BFD) on the company's router with a detection minimum interval of 300 ms and a BFD liveness detection multiplier of 3. A detection minimum interval of 300 ms means BFD control packets are sent every 300 milliseconds. A liveness detection multiplier of 3 means that if 3 consecutive BFD packets are missed, a failure is declared. Therefore, the maximum detection time would be: 300 ms × 3 = 900 ms, which is less than one second.

Step 4: AS Path Prepending for Failover Optimization (Optional)

• Apply a longer AS path on the passive link to ensure AWS prefers the active link.

VIF A (Primary for Production): AS_PATH 65000
VIF B (Backup for Production): AS_PATH 65000 65000        

Remark: When you have multiple VIFs in a Region, you can set the AS_PATH attribute to prioritize which interface AWS uses to route traffic. However, in example scenario, when the VIFs are in different Regions it is not possible.

Step 5: Advertising More Specific Routes

The more specific the prefix, the higher its priority in route selection. Ensure the primary connection advertises more specific prefixes. Example: Advertise 10.0.0.0/16 on both VIFs. Advertise 10.0.1.0/24 only on VIF A → AWS prefers VIF A for traffic to 10.0.1.0/24.

Configuring Active/Active Direct Connect Setup

Step 1: Configure Direct Connect Gateway

Same as Active/Passive setup.

Step 2: Configure BGP for Equal Preference

• Advertise the same prefixes from both VIF A and VIF B.
• Use identical BGP attributes (AS Path, MED, and Community Tags).

Apply BGP Community Tag: 7224:7300 on both VIFs.        

• AWS will load balance outbound traffic based on flow.

Step 3: Load Balancing with ECMP (Equal Cost Multi-Path)

• AWS distributes traffic per-flow using ECMP.
• Persistent connections could experience asymmetric routing, leading to issues with firewalls or session-based systems.

Testing and Monitoring

Recommended Tools

• AWS CloudWatch: Monitor Direct Connect metrics (e.g., link utilization, BGP session status).
• Traceroute & Pathping: Validate traffic flow.
• BGP Route Validation: Run show bgp on on-premises routers.

Failover Testing

• Simulate link failures (disable primary VIF) and observe BGP route changes.
• Check for session flaps or unexpected asymmetry.

Extending to Multi-Account Scenarios

For companies with multiple AWS accounts, AWS Transit Gateway can centralize Direct Connect access, improving manageability and security.

Summary of Methods for More Predictable Routing

Conclusion

By applying BGP community tags and attributes, organizations can control AWS Direct Connect traffic flow for Active/Active or Active/Passive configurations.

• Active/Passive: Ensures traffic symmetry and controlled failover.
• Active/Active: Maximizes bandwidth usage and resilience.

For further details, refer to the official AWS documentation: 👉 AWS Direct Connect Configuration Guide.

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