# CML + OSPF Triangle Lab

Python automation that builds a 3-router OSPF triangle in Cisco Modeling Labs (CML 2.x) end-to-end: create the lab, drop in three IOSv routers, wire them in a triangle, push day-0 configs with OSPF area 0 on every link, and start the lab. One command, reproducible topology.

Script: [`CML_OSPF_Basic_conf.py`](../scripts/CML_OSPF_Basic_conf.py)

## Topology

```
        R1 (1.1.1.1)
        /          \
 10.0.12.0/30   10.0.13.0/30
      /              \
   R2 (2.2.2.2) --- R3 (3.3.3.3)
          10.0.23.0/30
```

- Three IOSv routers: `R1`, `R2`, `R3`
- Three `/30` point-to-point links in a triangle
- Loopback0 on each router (`1.1.1.1`, `2.2.2.2`, `3.3.3.3`) advertised into OSPF
- All links in OSPF **area 0** (single area, no summarisation)

## Prerequisites

- A reachable CML 2.x controller (tested against 2.7)
- The `iosv` node definition installed on the controller
- Python 3.9+ and the official CML client:

```bash
pip install virl2-client
```

## Configure credentials

Set via environment variables (preferred) or edit the constants near the top of the script:

```bash
export CML_URL=https://cml.example.com
export CML_USERNAME=admin
export CML_PASSWORD='changeme'
```

> `ssl_verify=False` is set in the script for lab use. Flip to `True` and trust the CA when pointing at a real controller.

## Run it

```bash
python CML_OSPF_Basic_conf.py
```

Expected output:

```
Created lab '3-Router OSPF Triangle' (id=<uuid>)
Nodes and links created. Starting lab...
Lab is running.

Verify once routers boot (~1-2 min):
  R1# show ip ospf neighbor
  R1# show ip route ospf
  R1# ping 3.3.3.3 source 1.1.1.1
```

The lab appears in the CML UI with the three nodes laid out as a triangle:

![CML workbench view after running the script](../guide_images/CML_Labs/OSPF-basic/Lab-setup-post-script.png)

## What the script actually does

1. **Connects** to CML using `virl2_client.ClientLibrary` and waits for the controller to report ready.
2. **Creates a lab** titled *3-Router OSPF Triangle*.
3. **Creates three `iosv` nodes** (`R1`, `R2`, `R3`) at fixed coordinates so the layout is always identical.
4. **Assigns day-0 configs** to each node as a single multi-line string — interfaces, loopback, and `router ospf 1` stanza.
5. **Pads physical interfaces**. IOSv nodes are created with `Gi0/0` only; the helper `ensure_interfaces()` calls `create_interface()` until each node has three slots (`Gi0/0`, `Gi0/1`, `Gi0/2`).
6. **Wires the triangle** using `lab.create_link()` against specific `physical_interfaces[n]` so the slot numbers line up with what the day-0 configs expect.
7. **Starts the lab** — nodes boot and load their configs.

## Verify OSPF convergence

Once nodes boot (~1–2 minutes), open a console to R1 and check neighbors and routes:

```text
R1# show ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           1   FULL/BDR        00:00:35    10.0.12.2       GigabitEthernet0/1
3.3.3.3           1   FULL/BDR        00:00:38    10.0.13.2       GigabitEthernet0/2

R1# show ip route ospf
     2.0.0.0/32 is subnetted, 1 subnets
O       2.2.2.2 [110/2] via 10.0.12.2, ...
     3.0.0.0/32 is subnetted, 1 subnets
O       3.3.3.3 [110/2] via 10.0.13.2, ...
O    10.0.23.0/30 [110/2] via 10.0.12.2, ...
                         [110/2] via 10.0.13.2, ...
```

End-to-end reachability across loopbacks confirms the control plane is working:

![OSPF neighbors + routes on R1 after convergence](../guide_images/CML_Labs/OSPF-basic/OSPF-configmation-CML.png)

## Extending the lab

Things to bolt on once the basic triangle is healthy:

- **More areas** — split one link into area 1, add ABR logic and inter-area summarisation (`area 1 range ...`).
- **Authentication** — MD5 or SHA on each interface: `ip ospf authentication message-digest`.
- **Timers** — dial down hello/dead for sub-second convergence; test with a link flap.
- **BFD** — enable BFD on the links and have OSPF register for fast failure detection.
- **Telemetry** — wire each router into the [observability stack](observability.md) via IOS-XR MDT (or SNMP for IOSv) and watch neighbor state flap in Grafana as you tear links down.

## Troubleshooting

- **`Node definition 'iosv' not found`** — install the IOSv image on the CML controller; `iosvl2` won't work (layer-2 only).
- **Interface index errors** — the script assumes `create_interface()` adds the next sequential slot. If your controller's node definition pre-creates more or fewer interfaces, adjust `ensure_interfaces(node, 3)`.
- **Neighbors stuck in `EXSTART`/`EXCHANGE`** — usually an MTU mismatch. Set matching `ip mtu 1500` on both ends or add `ip ospf mtu-ignore`.
- **No OSPF neighbors at all** — check the link came up at L1 (`show ip interface brief`) and that no subinterface or CDP-only VLAN tagging is in the way.