Why do vpn/application gateways need to be in their subnet?

hi Longb1​ That’s an excellent observation — and it’s true that Azure’s approach is a bit different from what we’re used to in traditional on-prem networks.

In Azure Virtual Networks, resources like VPN Gateways, Application Gateways, and Azure Firewalls are managed services that act as network virtual appliances, rather than simple interfaces within your subnet.

Why they need their own subnet:

Isolation for managed routing and scaling

Azure gateways aren’t regular VMs — they’re platform-managed resources. Placing them in a dedicated subnet allows Azure to fully control routing, scaling, and IP allocation without conflicting with your own workloads.

Reserved IP ranges for internal operations

The gateway subnet must have a few unused IPs (usually at least a /27 range) so that Azure can deploy internal control plane components, health probes, and HA pairs. That’s why you can’t use all IPs in that subnet — Azure reserves several.

Separation of responsibilities

Gateways handle sensitive operations (encryption, routing, traffic inspection), so isolating them reduces the blast radius of configuration or security issues in your main subnets.

Predictable routing behavior

Having a distinct subnet ensures Azure’s routing tables can always unambiguously identify the gateway’s next hop. If it shared a subnet with workloads, route propagation and effective routes could conflict.

Why the subnet is small

Azure usually asks for a /27 or larger subnet (e.g., 10.0.255.0/27) because that provides enough IPs for HA, future scaling, and reserved system addresses — but it’s still small enough not to waste address space.