Budget Application Gateway v2 subnet addresses for peak instance count

Source facts

Azure reserves five addresses in each subnet. Application Gateway additionally consumes an address for every instance and another for a private frontend configuration. Microsoft recommends a /24 for v2 growth and maintenance, while explicitly saying that size is not mandatory.

Application Gateway v2 instance addresses are managed by Azure and are not individually listed as NIC IP configurations. Microsoft directs owners to include them through capacity calculation rather than relying only on visible allocations. Microsoft Learn.

Applicability

Inventory every gateway sharing the dedicated subnet, each intended maximum instance count, and its private frontend configuration. Keep the v2 calculation separate from older deployment assumptions and unrelated subnet examples.

DSE recommendation

DSE recommends an address budget with explicit rows for reserved addresses, each gateway’s planned instances, and frontends. Compare it with the available subnet range before increasing scale settings or adding another gateway. Record the expected traffic-driven instance requirement and the owner approving remaining headroom.

Verification

Reconcile the budget with the actual gateway configuration and visible allocated addresses. In an approved test, observe a planned scale change and check that the application remains reachable. Treat a clean NIC listing as incomplete capacity evidence, and investigate any discrepancy before expanding production traffic.

Official references

Microsoft Learn: Azure Application Gateway infrastructure configuration. Source retrieved September 9, 2026.