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ExpressRoute Global Reach often causes confusion, because it’s not the same as ExpressRoute into vWAN or VNet peering.

• If you have two ExpressRoute circuits in different peering locations (e.g., one in London, one in Frankfurt) connected to your on-premises datacenters, they are not automatically connected to each other.
• By default:
  • London DC ↔ Azure (via ER circuit 1)
  • Frankfurt DC ↔ Azure (via ER circuit 2)
  • But London DC ↔ Frankfurt DC cannot talk directly via Microsoft’s backbone.
• If you need those two datacenters to exchange traffic, you’d normally have to backhaul through your own WAN or build additional connectivity (VPN, MPLS, SD-WAN, etc.).

• ExpressRoute Global Reach lets you connect two (or more) on-premises sites together via the Microsoft backbone, through their ER circuits.
• So, your London on-premises site can talk directly to Frankfurt on-premises site, riding Microsoft’s private backbone instead of your own WAN.

• Eliminates the need for a separate WAN/MPLS link between sites.
• Reduces latency (uses Microsoft’s global backbone).
• Simplifies routing: both sites learn each other’s prefixes via ER BGP.
• Still keeps Azure reachable via both ER circuits.

ExpressRoute Global Reach solves the problem of connecting your own on-premises datacenters (in different geographic locations) to each other over Microsoft’s private backbone, using their respective ExpressRoute circuits.

• ExpressRoute Documentation

The main portal for all things related to ExpressRoute, including Global Reach.

  Link: https://docs.microsoft.com/ro-ro/azure/expressroute/

• ExpressRoute Global Reach Overview

Detailed explanation of how Global Reach connects on-premises environments via Microsoft’s private backbone.

  Link: https://docs.microsoft.com/ro-ro/azure/expressroute/expressroute-global-reach

• Tutorial: Peer On-Premises Environments to Azure VMware Solution

Practical guide showing how to use Global Reach to connect on-premises networks to Azure VMware Solution.

  Link: https://docs.microsoft.com/vi-vn/azure/azure-vmware/tutorial-expressroute-global-reach-private-cloud