azure-network-calculator

name	azure-network-calculator
description	Azure network planning — CIDR calculation, subnet allocation, VNet sizing, IP address planning, snet layout, network capacity, Azure networking, hub-spoke topology. USE WHEN CIDR, subnet, VNet, snet, network planning, IP address, Azure networking, calculate network, plan network, validate CIDR, network capacity, address space.

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

---

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.