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azure-network-calculator

azure-network-calculator

github.com/julianobarbosaCloud & DevOps1454 installsUpdated 2d ago
Repository

About azure-network-calculator

azure-network-calculator is a skill for planning Azure hub-spoke networks through CIDR calculations, subnet allocation, and Terraform code generation. It provides workflows for network planning, overlap checks, and capacity estimates.

Key features

  1. 01Plan VNet and subnet layouts
  2. 02Check CIDR allocation overlaps
  3. 03Calculate subscription and VNet capacity
  4. 04Generate Terraform network code
  5. 05Apply organization-specific customizations

Use cases

  1. 01Planning VNets and subnets for a resource group
  2. 02Checking CIDRs against existing allocations
  3. 03Reviewing remaining subscription or VNet capacity

Install

Copy the command and run it in a terminal.

$npx skills add https://github.com/julianobarbosa/claude-code-skills --skill azure-network-calculator

After installing, type/azure-network-calculatorin Claude Code to confirm it loaded.

Bundled files

References and scripts installed along with SKILL.md.

SubnetTemplates.md
TerraformSnippets.md
Workflows/
CalculateCapacity.md
PlanNetwork.md
ValidateCidr.md

Details

From the project README

Customization

Before executing, check for user customizations at: ~/.claude/skills/PAI/USER/SKILLCUSTOMIZATIONS/azure-network-calculator-skill/

If this directory exists, load and apply any PREFERENCES.md, configurations, or resources found there. These override default behavior. If the directory does not exist, proceed with skill defaults.

MANDATORY: Voice Notification (REQUIRED BEFORE ANY ACTION)

You MUST send this notification BEFORE doing anything else when this skill is invoked.

  1. Send voice notification:

    curl -s -X POST http://localhost:8888/notify \
  -H "Content-Type: application/json" \
  -d '{"message": "Running the WORKFLOWNAME workflow in the azure-network-calculator-skill skill to ACTION"}' \
  > /dev/null 2>&1 &

  2. Output text notification:

    Running the **WorkflowName** workflow in the **azure-network-calculator-skill** skill to ACTION...

This is not optional. Execute this curl command immediately upon skill invocation.

azure-network-calculator-skill

Automates CIDR calculation, subnet allocation, and Terraform code generation for your organization's Azure hub-spoke infrastructure.

Workflow Routing

IntentWorkflowDescription
Plan a VNet + subnets for a new resource groupPlanNetworkDesign complete network layout with Terraform
Check if a CIDR overlaps existing allocationsValidateCidrOverlap detection against master allocation
Show remaining capacity in a subscription/VNetCalculateCapacityAvailable /20 and /24 blocks

If the user's intent is ambiguous, ask which workflow to run.

Quick Reference

CIDR Hierarchy
/13  (subscription)  = 524,288 addresses = 128 x /20 VNets
/20  (VNet)          =   4,096 addresses =  16 x /24 subnets
/24  (subnet)        =     256 addresses =     251 usable (Azure reserves 5)
/22  (large subnet)  =   1,024 addresses =   1,019 usable
/27  (gateway)       =      32 addresses =      27 usable
/26  (firewall)      =      64 addresses =      59 usable
VNet Index Formula
VNet[i] address = subscription_base + (i * 4096)    # 4096 = 2^(32-20)
VNet[i] CIDR    = calculated_address/20

Each /13 subscription holds exactly 128 /20 VNets (index 0-127).

Azure Reserved IPs (5 per subnet)
OffsetPurpose
+0Network address
+1Default gateway
+2DNS mapping
+3DNS mapping
LastBroadcast
Naming Convention
snet-{purpose}-{rg}-{env}-{region}
vnet-{rg}-{env}-{region}
nsg-{purpose}-{rg}-{env}-{region}
natg-{rg}-{env}-{region}

Where {rg} is the resource group name (without rg-example- prefix), {env} is dev/hlg/prd, {region} is the shortcode (e.g., eus).

Context Files

FilePurpose
your CIDR master allocation (maintained outside this skill)All 16 subscriptions, known VNets, formulas
SubnetTemplates.md4 workload archetype subnet layouts
TerraformSnippets.mdAVM module HCL matching repo patterns

Gotchas

  • Azure reserves 5 IPs per subnet (network, gateway, DHCP, broadcast + 1 reserved): /29 has 3 usable, not 5; /28 has 11, not 13.
  • NSG rule count cap: 1000 per NSG — ASGs reduce rule count but introduce coupling between resource groups.
  • VNet peering doesn't support transitive routing — hub-spoke designs need Azure Firewall or NVA as an explicit hop; a hub-as-router assumption fails.
  • IPv6 dual-stack on AKS: requires preview feature flag; subnet calculations must size both v4 AND v6 explicitly.
  • Subnet delegation locks the subnet — once delegated to a service (e.g., AKS, App Service), it can't be undelegated without recreating.

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