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Azure Paired Regions and Cross-Region Resilience

For resilience beyond a single Azure location, you can connect IZO™+ Multi Cloud Connect to more than one Azure location or region. Tata Communications establishes the interconnects and applies BGP attributes so one metro is primary and the others are standby. Plan for the added latency on the longer path.  

Single-metro resilience vs cross-region resilience

By default, an Azure connection is already resilient within a metro: Tata Communications establishes dual interconnects with Microsoft and creates your circuit over both, with dual BGP sessions to the two MSEE routers. A single device or link failure within the metro fails over automatically.

Cross-region resilience goes a step further by placing your primary and secondary circuits in different Azure metros. If an entire metro becomes unavailable, traffic continues via the circuit in the other metro.

How cross-region resilience is built

Tata Communications has interconnects with Microsoft in multiple metros worldwide. To build cross-region resilience, you create a primary ExpressRoute circuit in one metro and a secondary circuit in another, and Tata Communications applies BGP attributes so the primary metro is preferred and the secondary takes over only on failure. For designs with more than two circuits, the same approach extends to tertiary and quaternary paths, each at a lower preference. The full Local Preference / AS-PATH scheme is on High Availability for Azure.

Azure’s view, and latency

Two points to plan around:

  • Active/active on the Azure side. Microsoft treats the primary, secondary, tertiary and quaternary circuits as active/active. Tata Communications applies the BGP attributes that make them behave as active/standby on the network path.

  • Latency increases with distance. Using a second metro for resilience means the backup path is geographically longer, so latency on that path will be higher. Where the workload is latency-sensitive, account for this in failover testing.

      A word on “paired regions”

      Microsoft also has a concept of Azure region pairs, used for certain platform-level replication and recovery features. That is an Azure-platform construct configured in Azure - it is separate from the network-path resilience described here, which is about how your ExpressRoute circuits and routing are arranged.

      What’s on the Azure side

      Creating the ExpressRoute circuits, choosing peering locations, and configuring routing and failover within Azure are done in your Azure portal.

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