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High Availability for Azure ExpressRoute

IZO™+ Multi Cloud Connect supports three ExpressRoute resiliency tiers, aligned to Microsoft’s resiliency architecture: Standard, High (ExpressRoute Metro), and Maximum.  

Standard resiliency is provided by default through dual MSEE peering at a single Azure metro. High resiliency (ExpressRoute Metro) adds a second circuit across two data centers within the same metro. Maximum resiliency places circuits across two distinct locations or Azure regions for site diversity. Across all tiers, Tata Communications applies BGP path control so redundant circuits behave as active/standby.  

Resiliency tiers

Standard resiliency (default)

A single ExpressRoute circuit with dual interconnects to the two MSEE routers within the same Azure peering location. Failover is automatic via BGP. This tier is included with every ExpressRoute circuit and needs no extra provisioning beyond configuring both BGP sessions on your CPE. Each circuit includes primary and secondary connectivity to the two MSEE routers within the peering location.

High resiliency (ExpressRoute Metro)

Two ExpressRoute circuits across different data centers within the same Azure metro. ExpressRoute Metro provides site-level redundancy by distributing the connection across two physically distinct locations within the metro. It suits business-critical and mission-critical workloads operating within a single Azure region.

Maximum resiliency

Maximum resiliency places a pair of ExpressRoute circuits across two distinct locations, or across distinct Azure regions, for full site diversity – for example Singapore and Seattle – with primary, secondary, tertiary and quaternary roles across up to four circuits. This tier extends resiliency beyond a single metro. Cross-metro paths introduce additional latency due to the geographical distance, so plan for it in latency-sensitive designs.

Path control across resiliency tiers

Microsoft treats redundant ExpressRoute circuits as active/active. Tata Communications applies BGP Local Preference and AS-PATH prepending to make them behave as active/standby on the network path. 

Across all tiers, Tata Communications applies path control on its side so redundant circuits behave as active/standby, and aligns the preference with your on-premises routing policy – agree the intended behaviour with your account team.

BFD (Bidirectional Forwarding Detection)

For sub-second failure detection on BGP sessions, BFD is supported: hello interval 300 ms, multiplier 3, giving failure detection in approximately 900 ms. Apply identical BFD parameters on both sides.

What sits with you (customer-side)

The following are the customer’s responsibility and not part of Tata Communications’ delivery:

  • CPE redundancy – provision redundant CPE so a single CPE failure does not eliminate access to ExpressRoute.

  • On-premises connectivity diversity – ensure your CPEs reach the Tata Communications MPLS Network over diverse last-mile paths.

  • Application-level failover – for Maximum resiliency, application-level traffic engineering (Azure Front Door, Traffic Manager, DNS) handles cross-region steering.

  • Workload deployment across regions – replicating workloads, data and configuration across Azure regions.

          Capacity planning across resiliency tiers

          When a circuit failure shifts traffic to the surviving circuit(s), those circuits carry the full load. Size accordingly: for active/standby deployments (the recommended pattern), each circuit must support peak traffic, not half – if peak is 4 Gbps, provision each circuit at 4 Gbps. Bandwidth changes within the same SKU are non-disruptive.

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