Prevent Assignment of Reserved CIDRs to Subnets #522
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Addition of new policy definition under /Network, which facilitates blocking the use of reserved ranges - ideal in enterprise environments where ranges have/are being reserved for specific use-cases. Users can leverage exemptions or exclusions to facilitate subnet deployment; if Azure Policy becomes identity aware in the future, too, there is room for platform-team exclusions, etc.
From `azurepolicy.json`, addition of `Disabled` as a valid parameter.
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Overview
This PR introduces a new Azure Policy definition as part of /Network.
The policy enables for CIDRs to be configured as non-usable by subnets; this can be useful in self-governing teams where a large range is allocated - but wish to earmark portions for specific purposes, such as future expansion, shared services, etc.
Problem Statement
In enterprise environments with decentralized subscription ownership, teams often receive large IP address allocations to manage independently. Without guardrails, there's a risk that subnets could inadvertently consume IP ranges earmarked for,
What the Policy Does
This policy uses
ipRangeContainsto perform bi-directional overlap detection.The intent is for this to be used in combination with "Exemptions", to provide just-in-time provisioning ability - whilst providing a hard guardrail.
If Azure Policy becomes identity-aware in the future, there is also scope for this to be used such that only X user may leverage specific ranges - useful in platform-team scenarios.