Add Peering Does Not Detect Gateway Subnet

Question

Repro 1. Via Azure Portal Add Vnet 2. Go Back into VNet just created and add Gateway Subnet. 3. From within same VNet try to add Peering, select peer Vnet and check "Allow gateway transit" checkbox.

Results - "Neither vnet-xxx nor vnet-yyy has a gateway configured. The gateway transit setting requires there to be a gateway in one virtual network in the peering. Please unselect the gateway transit setting to continue, or navigate to one of the virtual networks and add a gateway."

I have many other VNets and peering setup in the same manner and they all work. Going into the vnet peering configuration I can see the same error message however the checkbox is checked and it works.

The UI for adding a peering appears to have changed since I have added a Vnet and peering as I have never seen this error message prior using the old configuration UI for a peering.

FWIW I am trying to create a Vnet to be used by an app service that will peer to a Vnet that I have my managed SQL connected.

Answer 1

As the error message indicates that you have to have a gateway configured in one of the peering VNets when enabling the gateway transit. Only adding Gateway Subnet is not the process, you have to deploy a VPN gateway in the VNet in this case.

If you want to use VNet integration(add VNet preview), No gateway is required to use it and web app and VNet must be in the same region. But it seems that you do not use gateway transit due to lack of gateway configured in this case. Document just states this,

If you are using peering with the regional VNet Integration, you do not need to do any additional configuration.

It indicates that only existing VNet supports gateway transit currently. Not sure new VNet integration will support this feature in the future since it's still in preview. Additionally, you can get more details from another question about existing VNet integration and VNet peering I answered.