Create README.md for Create_Fabric script

utilities/Create_Fabric/README.md

@@ -0,0 +1,61 @@
+# Description
+
+Here’s a high-level tour of the repository and how its pieces fit together:
+
+## 1. Top-level scripts
+- **main.py**
+  - Entry point for VXLAN-Fabric creation.
+  - Prompts for NetBox URL/token, number of buildings, and device-type slugs.
+  - Validates input, connects to NetBox, builds a `FabricConfig`, and invokes `VXLANFabricCreator.create_fabric()`.
+  - Logs out the new site, spines, leaves and access switches.
+
+- **add_customers.py**
+  - Entry point for “customer” provisioning under an existing Fabric.
+  - Prompts for NetBox URL/token and customer details (name, VLAN/VNI, locations).
+  - Creates a tenant, assigns selected locations, allocates a /24 prefix, configures VLAN/L2VPN/VXLAN, and tags client interfaces on leaf switches.
+
+## 2. Configuration & constants
+- **config.py**
+  - Dataclasses and Enums defining:
+    - Interface types (QSFP, SFP, virtual…)
+    - Device roles (spine/leaf/access)
+    - IP-prefix roles (underlay, loopback)
+    - Default ASNs
+  - `FabricConfig` dataclass holds all parameters for fabric build.
+
+## 3. Exceptions
+- **exceptions.py**
+  - Custom exception hierarchy:
+    - `FabricError` base class
+    - `DeviceCreationError`, `IPAllocationError`, `CablingError` for granular error handling.
+
+## 4. NetBox API backend
+- **helpers/netbox_backend.py**
+  - `NetBoxBackend` wraps `pynetbox` and exposes:
+    - Tenant, Site, Device, VLAN, L2VPN, VXLAN-termination CRUD
+    - Interface management and cabling
+    - Prefix allocation and IP assignment
+    - Custom-fields saving and cleanup routines
+  - Uniform error-handler decorator logs errors and returns `None`.
+
+## 5. Fabric-creator core
+- **fabric_creator.py**
+  - `VXLANFabricCreator` orchestrates the fabric build:
+    1. `validate_prerequisites()`: Check roles, IP-roles, and device types exist in NetBox
+    2. `get_or_create_site()`: List or create a site
+    3. `create_spines()`: Always create two spine switches
+    4. `create_building_pair()`: For each building, create a leaf + access switch under a new Location
+    5. `setup_cabling()`: Cable leaf↔spines and leaf↔access ports
+    6. `setup_ip_addressing()`: Carve /31 underlay links and /32 loopbacks, assign to interfaces
+    7. `assign_asns()`: Stamp ASN custom-fields on spines and leaves
+    8. `create_fabric()`: Glue it all together, capture and return the site/devices created
+
+## 6. How to use
+- Ensure you have Python 3 and install `pynetbox`.
+- Export or enter your NetBox URL and API token.
+- Run `main.py` to spin up a new VXLAN fabric.
+- Run `add_customers.py` to onboard new tenants into an existing fabric.
+
+---
+
+This codebase gives you a higher-level, interactive automation layer atop NetBox, so you can script consistent VXLAN fabrics and customer provisioning without hand-crafting each object in the UI.