ExpressRoute Circuit Redundancy

This document explains how to implement redundancy for your ExpressRoute circuits to ensure high availability and minimize downtime for your critical network connections to Azure.

Why Redundancy is Important

ExpressRoute provides a private connection between your on-premises network and Microsoft Azure. To ensure business continuity, it's crucial to design your ExpressRoute connectivity for redundancy. This protects against single points of failure at the circuit, peering, or network level.

Redundancy Options

Azure offers several options for achieving ExpressRoute circuit redundancy:

1. Local Redundancy

This is the most basic level of redundancy, where you have multiple ExpressRoute circuits within the same Azure region. This protects against individual circuit failures but not against a regional outage.

Implementation: Deploy two or more ExpressRoute circuits in the same Azure region.
Use Case: Protecting against a single physical circuit or router failure.

2. Zonal Redundancy

This approach leverages Availability Zones within an Azure region. If your ExpressRoute provider supports Availability Zone connectivity, you can connect to different zones within the same region, providing resilience against zone-level failures.

Implementation: Work with your ExpressRoute provider to establish connections to different Availability Zones within an Azure region.
Use Case: Protecting against failures affecting a specific Availability Zone.

3. Cross-Region Redundancy

For disaster recovery and maximum availability, consider deploying ExpressRoute circuits in multiple Azure regions. This ensures that your applications and services remain accessible even if an entire Azure region becomes unavailable.

Implementation: Deploy ExpressRoute circuits in at least two different Azure regions. Ensure your on-premises network can route traffic to both regions.
Use Case: Disaster recovery and protecting against major regional outages.

4. Redundant Peering Locations

ExpressRoute circuits connect to Azure at specific peering locations. To add redundancy, you can provision circuits that connect to different, geographically diverse peering locations. This protects against issues at a specific colocation facility or peering exchange.

Implementation: Work with your ExpressRoute provider to choose different peering locations for your circuits.
Use Case: Protecting against failures at a specific network exchange point.

Implementing Redundancy

When designing your redundant ExpressRoute solution, consider the following:

Circuit Capacity: Ensure that each circuit has sufficient bandwidth to handle your traffic. In a failover scenario, the remaining active circuits must be able to absorb the load.
Peering Configuration: Configure dynamic routing (BGP) on your connections. Ensure that your on-premises routers and Azure virtual networks are configured to handle multiple paths and failover.
Route Advertisements: Carefully manage BGP route advertisements to ensure predictable failover behavior.
Testing: Regularly test your failover mechanisms to ensure they function as expected. Simulate circuit failures and verify that traffic is rerouted correctly.

Note: Consult with your ExpressRoute service provider to understand their redundancy capabilities and how they align with Azure's redundancy options.

High Availability with ExpressRoute Premium

For scenarios requiring global connectivity and enhanced routing capabilities, ExpressRoute Premium offers features that can complement redundancy strategies, such as:

Global Reach: Allows you to connect your on-premises networks across different Azure regions.
Increased Number of Peering Locations: Access to more peering locations for diverse connectivity.

Conclusion

Implementing robust ExpressRoute circuit redundancy is essential for maintaining the availability and reliability of your Azure connectivity. By carefully planning and implementing one or more of the redundancy options discussed, you can significantly reduce the risk of network-related downtime.