Missing subnet referenced 'GatewaySubnet' in virtual network 'MyNetwork' - azure

Question

I've built a network in Azure that contains two subnets, Back and Front.
I'm now trying to create a gateway using Set-AzureVNetConfig but I'm getting a missing subnet called GatewaySubnet. This word does not exist anywhere in my scripts and Googling the word returns no results so it cannot be a reserved word.
<NetworkConfiguration xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://schemas.microsoft.com/ServiceHosting/2011/07/NetworkConfiguration">
<VirtualNetworkConfiguration>
<Dns />
<LocalNetworkSites>
<LocalNetworkSite name="lnt">
<AddressSpace>
<AddressPrefix>10.55.10.0/24</AddressPrefix>
</AddressSpace>
<VPNGatewayAddress>1.2.3.4</VPNGatewayAddress>
</LocalNetworkSite>
</LocalNetworkSites>
<VirtualNetworkSites>
<VirtualNetworkSite name="net" AffinityGroup="ag">
<AddressSpace>
<AddressPrefix>10.10.0.0/16</AddressPrefix>
</AddressSpace>
<Subnets>
<Subnet name="Front">
<AddressPrefix>10.10.1.0/24</AddressPrefix>
</Subnet>
<Subnet name="Back">
<AddressPrefix>10.10.2.0/24</AddressPrefix>
</Subnet>
</Subnets>
<Gateway>
<ConnectionsToLocalNetwork>
<LocalNetworkSiteRef name="lnt" />
</ConnectionsToLocalNetwork>
</Gateway>
</VirtualNetworkSite>
</VirtualNetworkSites>
</VirtualNetworkConfiguration>
Why does Azure think my config file is missing a subnet called GatewaySubnet?

Answer 1

Taking a guess that this is a point-to-site network (and it looks like one). If that's the case, you need to add the gateway subnet (you can see this in the portal, for point-to-site network configuration). You can add this from the Configure tab: scroll to the bottom and look at virtual network address spaces - you'll see a button to add the gateway subnet. If you do this, and then export your network, you'll see a GatewaySubnet element.