# YANG Module

This module provides YANG path constants and utilities for managing Arista EVPN-VXLAN fabrics via gNMI.

## Overview

The module contains validated gNMI paths for Arista EOS 4.35.0F, organized by feature:

| Class         | Model      | Description                     |
| ------------- | ---------- | ------------------------------- |
| `Interfaces`  | OpenConfig | Physical and logical interfaces |
| `Loopbacks`   | OpenConfig | Loopback interfaces             |
| `VLANs`       | OpenConfig | VLAN configuration and SVIs     |
| `BGP`         | OpenConfig | BGP global, neighbors, AFI-SAFI |
| `VXLAN`       | Arista Exp | VXLAN VNI mappings              |
| `MLAG`        | Arista Exp | MLAG config (state via eAPI)    |
| `EVPN`        | Arista Exp | EVPN instances (state via eAPI) |
| `PortChannel` | OpenConfig | LAG/Port-Channel                |
| `System`      | OpenConfig | System configuration            |

## Installation

```python
from yang.paths import Interfaces, BGP, VXLAN
```

## Usage Examples

### Interfaces

```python
from yang.paths import Interfaces

# Get all interfaces
path = Interfaces.ROOT
# -> "/interfaces/interface"

# Get specific interface
path = Interfaces.interface("Ethernet1")
# -> "/interfaces/interface[name=Ethernet1]"

# Get interface state
path = Interfaces.state("Ethernet1")
# -> "/interfaces/interface[name=Ethernet1]/state"

# Get operational status
path = Interfaces.oper_status("Ethernet1")
# -> "/interfaces/interface[name=Ethernet1]/state/oper-status"
```

### Loopbacks

```python
from yang.paths import Loopbacks

# Get loopback interface
path = Loopbacks.interface(0)
# -> "/interfaces/interface[name=Loopback0]"

# Use predefined constants
path = Loopbacks.LOOPBACK0  # Router ID
path = Loopbacks.LOOPBACK1  # VTEP source
```

### VLANs

```python
from yang.paths import VLANs

# Get all VLANs
path = VLANs.ROOT
# -> "/network-instances/network-instance[name=default]/vlans/vlan"

# Get specific VLAN
path = VLANs.vlan(40)
# -> "/network-instances/network-instance[name=default]/vlans/vlan[vlan-id=40]"

# Get SVI interface
path = VLANs.svi(40)
# -> "/interfaces/interface[name=Vlan40]"
```

### BGP

```python
from yang.paths import BGP, AfiSafi

# Get all neighbors
path = BGP.NEIGHBORS
# -> "/network-instances/.../bgp/neighbors/neighbor"

# Get specific neighbor
path = BGP.neighbor("10.0.1.0")

# Get neighbor session state
path = BGP.neighbor_session_state("10.0.1.0")

# Get EVPN AFI-SAFI for neighbor
path = BGP.neighbor_afi_safi("10.0.250.1", AfiSafi.L2VPN_EVPN)
```

### VXLAN

```python
from yang.paths import VXLAN

# Get all VNI mappings
path = VXLAN.VLAN_TO_VNIS
# -> "/interfaces/interface[name=Vxlan1]/arista-vxlan/vlan-to-vnis"

# Get specific VNI
path = VXLAN.vlan_to_vni(40)
# -> ".../vlan-to-vnis/vlan-to-vni[vlan=40]"

# Get L3 VNI (VRF-to-VNI)
path = VXLAN.vrf_to_vni("gold")
# -> ".../vrf-to-vnis/vrf-to-vni[vrf=gold]"

# Get VTEP source interface config
path = VXLAN.SOURCE_INTERFACE
```

### MLAG

```python
from yang.paths import MLAG

# Get MLAG config
path = MLAG.CONFIG
# -> "/arista/eos/mlag/config"

# ⚠️ Note: MLAG state is NOT available via gNMI
# Use eAPI for: show mlag
```

### EVPN

```python
from yang.paths import EVPN

# Get all EVPN instances
path = EVPN.INSTANCES
# -> "/arista/eos/evpn/evpn-instances"

# Get specific instance
path = EVPN.instance("40")

# Get route-targets
path = EVPN.route_target("40")

# ⚠️ Note: EVPN state is NOT available via gNMI
# Use eAPI for: show bgp evpn
```

### Port-Channel

```python
from yang.paths import PortChannel

# Get port-channel interface
path = PortChannel.interface(999)
# -> "/interfaces/interface[name=Port-Channel999]"

# Get LAG aggregation config
path = PortChannel.aggregation(999)
```

### Subscriptions

```python
from yang.paths import FabricSubscriptions, SubscriptionPath

# Get pre-built subscription paths
for sub in FabricSubscriptions.all():
    print(f"Path: {sub.path}, Mode: {sub.mode}")

# Individual subscriptions
sub = FabricSubscriptions.INTERFACE_STATE
sub = FabricSubscriptions.BGP_SESSIONS
sub = FabricSubscriptions.VXLAN_VNIS

# Create custom subscription
custom = SubscriptionPath(
    path="/interfaces/interface[name=Ethernet1]/state",
    mode="on-change"
)
```

## Limitations

| Feature | Config | State | Notes              |
| ------- | ------ | ----- | ------------------ |
| MLAG    | ✅      | ❌     | Use eAPI for state |
| EVPN    | ✅      | ❌     | Use eAPI for state |

## References

- [Full YANG Paths Documentation](../../docs/yang-paths.md)
- [Arista YANG Models](https://github.com/aristanetworks/yang/tree/master/EOS-4.35.0F)
- [OpenConfig Models](https://github.com/openconfig/public)