Azure network calculator

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

Intent	Workflow	Description
Plan a VNet + subnets for a new resource group	PlanNetwork	Design complete network layout with Terraform
Check if a CIDR overlaps existing allocations	ValidateCidr	Overlap detection against master allocation
Show remaining capacity in a subscription/VNet	CalculateCapacity	Available /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)

Offset	Purpose
+0	Network address
+1	Default gateway
+2	DNS mapping
+3	DNS mapping
Last	Broadcast

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

File	Purpose
your CIDR master allocation (maintained outside this skill)	All 16 subscriptions, known VNets, formulas
SubnetTemplates.md	4 workload archetype subnet layouts
TerraformSnippets.md	AVM module HCL matching repo patterns

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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.