| 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.
-
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 &
-
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.
