Hello @Pierrick Morel ,
Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.
Yes, it is possible to link the two ExpressRoute gateways to the same ExpressRoute circuit as shown in your diagram.
However, there is a documented limitation in this setup regarding the inter-vHub VNet-to-VNet connectivity as below:
When two hubs (hub 1 and 2) are connected and there is an ExpressRoute circuit connected as a bow-tie to both the hubs, the current behavior is to prefer the ExpressRoute circuit path over hub-to-hub for VNet-to-VNet connectivity (i.e. the path for a VNet connected to hub 1 to reach a VNet connected in hub 2). However, this is not encouraged in a Virtual WAN setup. To resolve this, you can do one of two things:
1) Configure multiple ExpressRoute circuits (different providers) to connect to one hub and use the hub-to-hub connectivity provided by Virtual WAN for inter-region traffic flows.
2) Contact the product team to take part in the gated public preview. In this preview, traffic between the 2 hubs traverses through the Azure Virtual WAN router in each hub and uses a hub-to-hub path instead of the ExpressRoute path (which traverses through the Microsoft edge routers/MSEE). To use this feature during preview, email email@example.com with the Virtual WAN IDs, Subscription ID, and the Azure region. Expect a response within 48 business hours (Monday-Friday) with confirmation that the feature is enabled.
Kindly let us know if the above helps or you need further assistance on this issue.
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