Azure App Gateway V2 cannot be configured with NSG

Question

I have provisioned App Gateway with WAF V2 SKU. Then, I have configured back-end pool to point to WebApp and added IP restrictions to allow only traffic from WAF IP. Then, i am attempting to add NSG to the provisioned Subnet to further restrict traffic to the Frontend IP address. I am getting an error (see below). Per Application Gateway FAQ this should be possible, but having trouble. Here is are the details of the deployment error:

Network security group /subscriptions/49c19f96-135d-4599-ae34-fd9087ce2bf8/resourceGroups/dbt-sc-platform-rg/providers/Microsoft.Network/networkSecurityGroups/BannerCIDRNsg blocks incoming internet traffic on ports 65200 - 65535 to subnet /subscriptions/49c19f96-135d-4599-ae34-fd9087ce2bf8/resourceGroups/dbt-sc-platform-rg/providers/Microsoft.Network/virtualNetworks/dbt-sc-platform-rg/subnets/default, associated with Application Gateway /subscriptions/49c19f96-135d-4599-ae34-fd9087ce2bf8/resourceGroups/dbt-sc-platform-rg/providers/Microsoft.Network/applicationGateways/dbt-sc-appgw. This is not permitted for Application Gateways that have V2 Sku.

Answer 1

The error message displays that you need to add incoming internet traffic on ports 65200 - 65535 to subnet-default in your Network security group-BannerCIDRNsg.

Per Application Gateway FAQ, you can whitelist Application Gateway access to a few source IPs.

This scenario can be done using NSGs on Application Gateway subnet. The following restrictions should be put on the subnet in the listed order of priority:

Allow incoming traffic from source IP/IP range.

Exceptions must be put in for incoming traffic on ports 65503-65534 for the Application Gateway V1 SKU and ports 65200 - 65535 for the V2 SKU. This port-range is required for Azure infrastructure communication. They are protected (locked down) by Azure certificates. Without proper certificates, external entities, including the customers of those gateways, will not be able to initiate any changes on those endpoints.

Allow incoming Azure Load Balancer probes (AzureLoadBalancer tag) and inbound virtual network traffic (VirtualNetwork tag) on the NSG.

Block all other incoming traffic with a Deny all rule.

Allow outbound traffic to the internet for all destinations.

Answer 2

I was getting the error message "Subnet associated to gateway with v2 sku" when trying to associate a subnet containing a Gateway V2 WAF to an existing NSG.

Strangely though it was no problem navigating to the VNET -> SubNet and after clicking the given SubNet then associating the NSG to that SubNet.

Answer 3

I want to add on @Nancy's answer, that actually, as per the documentation, there is no need to allow traffic from Any protocol. Allowing TCP traffic is enough.

There is also no need to allow traffic from Any source, it is sufficient to allow traffic from GatewayManager service tag.

You must allow incoming Internet traffic on TCP ports 65503-65534 for the Application Gateway v1 SKU, and TCP ports 65200-65535 for the v2 SKU with the destination subnet as Any and source as GatewayManager service tag. This port range is required for Azure infrastructure communication.

So, I created the security rule as follows:

It should also be noted that:

These ports are protected (locked down) by Azure certificates. External entities, including the customers of those gateways, can't communicate on these endpoints.