anonymous user, For Hub private address space the minimum address space is /24 to create a hub. If you use anything in the range from /25 to /32, it will produce an error during creation. You don't need to explicitly plan the subnet address space for the services in the virtual hub. Because Azure Virtual WAN is a managed service, it creates the appropriate subnets in the virtual hub for the different gateways/services (for example, VPN gateways, ExpressRoute gateways, User VPN point-to-site gateways, Firewall, routing, and etc.).
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