# Fabric Standardization — Small EVPN-VXLAN Data Centers

> **Status**: Draft — Phase 0 (#31)
> **Scope**: POC for small data centers (2-4 spines, up to 24 leaf pairs)
> **Parent**: Epic #30

---

## 1. Device model

### 1.1 Reference platform — Arista 7050SX3-48YC12

All fabric devices (spines and leafs) use the same hardware model:

| Attribute | Value |
|-----------|-------|
| Model | 7050SX3-48YC12 |
| 25G SFP28 ports | 48 (Ethernet1–48) |
| 100G QSFP100 ports | 12 (Ethernet49–60) |
| Total ports | 60 |

Port banks are physically separated, enabling clean role assignment with no overlap between host-facing and fabric traffic.

### 1.2 Port role assignment — Production

**Spine (production):**

| Port bank | Role | Details |
|-----------|------|---------|
| Ethernet1–48 (25G) | Leaf downlinks | 1 port per leaf, routed P2P /31, MTU 9214 |
| Ethernet49–60 (100G) | Reserved | Future: inter-spine links, DCI, monitoring |

**Leaf (production):**

| Port bank | Role | Details |
|-----------|------|---------|
| Ethernet1–48 (25G) | Host-facing | MLAG port-channels (trunk, LACP active) |
| Ethernet49 (100G) | MLAG peer-link | Port-Channel999 (trunk, trunk-group `mlag-peer`) |
| Ethernet50–{49+N_spines} (100G) | Spine uplinks | 1 per spine, routed P2P /31, MTU 9214 |
| Remaining 100G | Reserved | Future use |

### 1.3 Port role assignment — Containerlab (clab)

Containerlab uses the `ceos` image with a **fixed 12-port model** (Ethernet1–12, uniform speed). The production layout is compressed into 12 ports using a deterministic formula based on spine count:

| Parameter | Formula |
|-----------|---------|
| Spine uplinks | Last N ports: **Ethernet{13−N_spines}** through **Ethernet12** |
| MLAG peer-link | Port just before uplinks: **Ethernet{12−N_spines}** |
| Host-facing | All remaining: **Ethernet1** through **Ethernet{11−N_spines}** |
| Host port count | **12 − N_spines − 1** |

**Concrete layouts per spine count:**

| Spines | Host ports | MLAG port | Spine uplinks | Host count |
|--------|-----------|-----------|---------------|------------|
| 2 | Eth1–9 | Eth10 | Eth11 (S1), Eth12 (S2) | 9 |
| 3 | Eth1–8 | Eth9 | Eth10 (S1), Eth11 (S2), Eth12 (S3) | 8 |
| 4 | Eth1–7 | Eth8 | Eth9 (S1), Eth10 (S2), Eth11 (S3), Eth12 (S4) | 7 |

**Spine in clab:** all 12 ports are leaf downlinks (Ethernet1 → Leaf-01, Ethernet2 → Leaf-02, ...).

---

## 2. Topology constraints

### 2.1 Derived limits

All limits derive from the device model and the MLAG pairing rule (leafs always in pairs):

| Constraint | Production (7050SX3-48YC12) | Clab (12-port) | Source |
|------------|----------------------------|-----------------|--------|
| Min spines | 2 | 2 | Redundancy requirement |
| Max spines | 4 | 4 | Small DC scope (hardware allows more) |
| Max leafs per fabric | 48 | 12 | Spine downlink port count |
| Max leaf pairs per fabric | 24 | 6 | Max leafs ÷ 2 |
| Min leaf pairs per fabric | 1 | 1 | Minimum viable fabric |
| Max host ports per leaf | 48 | 12 − N_spines − 1 | Port bank size minus fabric ports |
| Spine uplinks per leaf | N_spines | N_spines | 1 uplink per spine |
| MLAG peer-link ports | 1 (100G) | 1 | Fixed: Po999 |

### 2.2 Validation rules

The fabric generator must enforce:

1. **N_spines ∈ {2, 3, 4}** — minimum 2 for redundancy, max 4 for small DC scope
2. **N_leafs is even** — leafs always come in MLAG pairs
3. **N_leafs ≥ 2** — at least 1 MLAG pair
4. **N_leafs ≤ spine downlink port count** — cannot exceed physical ports
5. **Every leaf connects to every spine** — full-mesh underlay
6. **Every spine connects to every leaf** — symmetric fabric

### 2.3 Spine layer
- Spines are **pure L3 routers** — no VTEPs, no VLANs, no MLAG
- Each spine connects to every leaf via a dedicated P2P link
- All spines share the same ASN within a fabric

### 2.4 Leaf layer
- Leafs always come in **MLAG pairs** (2 leafs = 1 VTEP)
- Each leaf connects to **all spines** via dedicated uplinks
- Each leaf pair shares a **VTEP loopback IP** (Loopback1)

### 2.5 Host connectivity
- Hosts connect **directly to leaf pairs** — no access switches
- Every host is **dual-homed** via MLAG (LACP active)
- Each host-facing port-channel gets a unique MLAG ID

### 2.6 POC defaults

For the initial POC, the following defaults apply:

| Parameter | Default | Notes |
|-----------|---------|-------|
| Spines | 2 | Minimum for redundancy |
| Leaf pairs | 3 (6 leafs) | Enough to validate multi-VTEP behavior |
| Platform | clab (ceos, 12 ports) | Production model as reference only |

---

## 3. Port assignment — Spine

Spines use sequential port mapping: one port per leaf, starting from Ethernet1.

| Port | Role | Connected to |
|------|------|-------------|
| Ethernet1 | Underlay downlink | Leaf-01 |
| Ethernet2 | Underlay downlink | Leaf-02 |
| ... | ... | ... |
| Ethernet{N_leafs} | Underlay downlink | Leaf-{N_leafs} |

**Production:** Ethernet1–48 (25G), remaining ports reserved.
**Clab:** Ethernet1–12, all available for downlinks.

All spine downlinks are:
- **Routed** (`no switchport`)
- **/31 P2P addressing**
- **MTU 9214** (jumbo frames for VXLAN encapsulation)

---

## 4. Port assignment — Leaf

### 4.1 Host-facing ports
- Each physical port maps to a Port-Channel
- Port-Channel number = MLAG ID = host index (e.g., host 01 → Po1, MLAG 1)
- Mode: `switchport mode trunk`
- VLANs: only the VLANs needed by the host
- LACP fallback enabled (timeout 5, individual)

### 4.2 MLAG peer-link
- Always **Port-Channel999**
- Trunk mode with trunk-group `mlag-peer`
- Spanning-tree link-type point-to-point
- Carries MLAG control traffic + VLANs 4090, 4091

**Production:** Ethernet49 (100G)
**Clab:** Ethernet{12−N_spines} (derived from formula in §1.3)

### 4.3 Spine uplinks
- One uplink per spine, routed P2P /31, MTU 9214
- Fixed mapping: uplink port index matches spine index

**Production:** Ethernet50 → Spine-01, Ethernet51 → Spine-02, ... Ethernet{49+N_spines} → Spine-{N_spines}
**Clab:** Ethernet{13−N_spines} → Spine-01, ..., Ethernet12 → Spine-{N_spines}

---

## 5. Naming conventions

### 5.1 Device hostname format

All device hostnames follow the pattern:

```
<SITE>-<ZONE>-<ROLE>-<ID>
```

| Field | Length | Description | Values |
|-------|--------|-------------|--------|
| `SITE` | 2 chars | City / location code (uppercase) | PA (Paris), LY (Lyon), MA (Marseille), LO (London)... |
| `ZONE` | 2-3 chars | Network area (uppercase) | DC (Datacenter), DR (Disaster Recovery), LAB (Lab), CO (Colocation) |
| `ROLE` | 4-5 chars | Device function (uppercase) | SPINE, LEAF, HOST |
| `ID` | 2 digits | Sequential number (zero-padded) | 01, 02, ..., 99 |

**Examples for Paris datacenter:**

| Device | Hostname |
|--------|----------|
| Spine 1 | `PA-DC-SPINE-01` |
| Spine 2 | `PA-DC-SPINE-02` |
| Leaf 1 (pair 1, primary) | `PA-DC-LEAF-01` |
| Leaf 2 (pair 1, secondary) | `PA-DC-LEAF-02` |
| Leaf 3 (pair 2, primary) | `PA-DC-LEAF-03` |
| Leaf 4 (pair 2, secondary) | `PA-DC-LEAF-04` |
| Host 1 | `PA-DC-HOST-01` |

**Examples for Lyon disaster recovery:**

| Device | Hostname |
|--------|----------|
| Spine 1 | `LY-DR-SPINE-01` |
| Leaf 1 | `LY-DR-LEAF-01` |

### 5.2 Leaf pairing rule

Leafs are numbered sequentially. **Odd = primary, even = secondary** within a pair:

| Pair | Primary | Secondary | VTEP |
|------|---------|-----------|------|
| 1 | `{SITE}-{ZONE}-LEAF-01` | `{SITE}-{ZONE}-LEAF-02` | VTEP 1 |
| 2 | `{SITE}-{ZONE}-LEAF-03` | `{SITE}-{ZONE}-LEAF-04` | VTEP 2 |
| 3 | `{SITE}-{ZONE}-LEAF-05` | `{SITE}-{ZONE}-LEAF-06` | VTEP 3 |
| 4 | `{SITE}-{ZONE}-LEAF-07` | `{SITE}-{ZONE}-LEAF-08` | VTEP 4 |

### 5.3 Fabric name

The fabric is identified by `{SITE}-{ZONE}` (lowercase in Infrahub objects):

| Infrahub object | Name | Example |
|----------------|------|---------|
| `InfraFabric` | `{site}-{zone}` | `pa-dc` |
| `LocationSite` | `{site}-{zone}` | `pa-dc` |

### 5.4 Interface descriptions

Interface descriptions reference the **full hostname** of the remote device:

| Interface | Description format | Example (on PA-DC-LEAF-01) |
|-----------|-------------------|----------------------------|
| Spine uplink | `to {REMOTE_HOSTNAME}` | `to PA-DC-SPINE-01` |
| MLAG peer-link | `mlag peer link` | `mlag peer link` |
| Host-facing | `to {HOST_HOSTNAME}` | `to PA-DC-HOST-01` |
| Loopback0 | `Router-ID` | `Router-ID` |
| Loopback1 | `VTEP` | `VTEP` |

On spines:

| Interface | Description format | Example (on PA-DC-SPINE-01) |
|-----------|-------------------|----------------------------|
| Downlink | `to {REMOTE_HOSTNAME}` | `to PA-DC-LEAF-01` |
| Loopback0 | `Router-ID` | `Router-ID` |

### 5.5 MLAG domain

| Parameter | Value | Notes |
|-----------|-------|-------|
| Domain ID | `{site}-{zone}-pair{NN}` | e.g., `pa-dc-pair01` — unique per MLAG pair |
| Peer-link | Port-Channel999 | Fixed |
| Peer-link VLAN | 4090 | Fixed |
| iBGP peering VLAN | 4091 | Fixed |

### 5.6 BGP descriptions

| Session type | Description format | Example |
|-------------|-------------------|---------|
| eBGP underlay | `underlay to {REMOTE_HOSTNAME}` | `underlay to PA-DC-SPINE-01` |
| iBGP MLAG peer | `ibgp to {REMOTE_HOSTNAME}` | `ibgp to PA-DC-LEAF-02` |
| EVPN overlay | `evpn to {REMOTE_HOSTNAME}` | `evpn to PA-DC-SPINE-01` |

### 5.7 IPAM identifiers (for resource pool idempotence)

All identifiers use **lowercase**, with the fabric name `{site}-{zone}`:

| Object | Identifier pattern | Example |
|--------|-------------------|---------|
| Site infra prefix | `site-{site}-{zone}-infra` | `site-pa-dc-infra` |
| Site services prefix | `site-{site}-{zone}-services` | `site-pa-dc-services` |
| Device loopback0 IP | `lo0-{site}-{zone}-{role}-{id}` | `lo0-pa-dc-leaf-01` |
| Device loopback1 IP | `lo1-{site}-{zone}-vtep{NN}` | `lo1-pa-dc-vtep01` |
| Underlay P2P /31 | `p2p-{site}-{zone}-spine{NN}-leaf{NN}` | `p2p-pa-dc-spine01-leaf01` |
| MLAG peer /31 | `mlag-peer-{site}-{zone}-pair{NN}` | `mlag-peer-pa-dc-pair01` |
| MLAG iBGP /31 | `mlag-ibgp-{site}-{zone}-pair{NN}` | `mlag-ibgp-pa-dc-pair01` |
| Leaf ASN | `asn-{site}-{zone}-pair{NN}` | `asn-pa-dc-pair01` |
| L2 VNI | `l2vni-{site}-{zone}-vlan{NNNN}` | `l2vni-pa-dc-vlan0040` |
| L3 VNI | `l3vni-{site}-{zone}-{vrf_name}` | `l3vni-pa-dc-gold` |

### 5.8 Site prefix registry

To avoid conflicts, site prefixes must be registered:

| Prefix | City | Country |
|--------|------|---------|
| PA | Paris | FR |
| LY | Lyon | FR |
| MA | Marseille | FR |
| LO | London | UK |
| FR | Frankfurt | DE |
| AM | Amsterdam | NL |

> This registry is maintained as a reference. The `SITE` code is stored on the `LocationSite` object in Infrahub.

---

## 6. IPAM — IP addressing plan

### 6.1 Design principle

Only the **two supernets** are fixed. All intermediate allocations (site prefixes, fabric pools, individual subnets) are delegated to **Infrahub's resource manager**, which picks the smallest available prefix that satisfies the request. Prefix sizes mentioned in this document are illustrative defaults — the generator requests a number of allocations from a pool and Infrahub handles sizing and placement.

### 6.2 Supernets (global, fixed)

| Role | Supernet | Description |
|------|----------|-------------|
| Infrastructure | `10.0.0.0/8` | Loopbacks, underlay, MLAG |
| Services | `172.16.0.0/12` | L2/L3 VXLAN user subnets |

These are the only hardcoded prefixes. Everything below is allocated dynamically.

### 6.3 Site allocation (from supernets)

Each site receives one prefix from each supernet, allocated by Infrahub:
- **1 prefix** from `10.0.0.0/8` for infrastructure (e.g., /16)
- **1 prefix** from `172.16.0.0/12` for services (e.g., /16)

### 6.4 Fabric pools (from site infra prefix)

The fabric generator creates pools within the site's infrastructure prefix. Each pool serves a specific role and allocates individual subnets on demand:

| Pool | Allocation unit | Pool type | Example size |
|------|-----------------|-----------|-------------|
| Loopback0 (router-id) | /32 per device | `CoreIPAddressPool` | /24 |
| Loopback1 (VTEP) | /32 per MLAG pair | `CoreIPAddressPool` | /24 |
| Underlay P2P | /31 per spine-leaf link | `CoreIPPrefixPool` | /24 or /23 |
| MLAG peer-link SVI | /31 per MLAG pair | `CoreIPPrefixPool` | /24 |
| MLAG iBGP peering | /31 per MLAG pair | `CoreIPPrefixPool` | /24 |

> **Example sizes are not prescriptive.** Infrahub allocates the parent prefix for each pool based on the number of resources requested. A 2-spine / 6-leaf fabric needs far fewer /31s than a 4-spine / 48-leaf fabric — the resource manager adapts accordingly.

### 6.5 Service pools (from site services prefix)

| Pool | Allocation unit | Pool type |
|------|-----------------|-----------|
| L2 VXLAN subnets | Per VLAN (e.g., /24) | `CoreIPPrefixPool` |
| L3 VXLAN subnets (VRF SVIs) | Per VRF SVI (e.g., /24) | `CoreIPPrefixPool` |

### 6.6 Special VLANs (reserved, not from pools)

| VLAN | Name | Purpose | Trunk group |
|------|------|---------|-------------|
| 4090 | mlag-peer | MLAG peer-link SVI | mlag-peer |
| 4091 | mlag-ibgp | MLAG iBGP peering | mlag-peer |

---

## 7. BGP — Autonomous System assignment

### 7.1 Spine ASN
- **Single ASN** shared by all spines in a fabric
- Defined as an attribute on `InfraFabric`
- Default for POC: **65000**

### 7.2 Leaf ASN
- **One ASN per MLAG pair** (iBGP within pair, eBGP to spines)
- Allocated from a `CoreNumberPool` (range: 65001–65099)
- Deterministic via identifier: `asn-{site}-{zone}-pair{NN}`

### 7.3 BGP configuration standards

| Parameter | Value | Notes |
|-----------|-------|-------|
| `no bgp default ipv4-unicast` | Always | Explicit activation per AFI |
| `bgp log-neighbor-changes` | Always | Operational visibility for BGP state transitions |
| `distance bgp` | `20 200 200` | eBGP preferred over iBGP |
| `maximum-paths` | `{N_spines × 2} ecmp 64` | Multi-path scaled to spine count (e.g., 2 spines → `4`, 4 spines → `8`) |
| `maximum-routes` | `12000 warning-only` | Per neighbor |
| `ebgp-multihop` | `3` | EVPN overlay (loopback peering) |
| `send-community extended` | Always | Required for EVPN route-targets |
| `next-hop-unchanged` | Spine EVPN peer-group | Preserve leaf next-hop in overlay |
| `next-hop-self` | Leaf iBGP peer-group | Required for iBGP convergence |

### 7.4 Peer groups (per device)

**Leaf peer groups:**

| Peer group | Type | Remote AS | Neighbors |
|------------|------|-----------|-----------|
| `underlay` | eBGP | spine ASN | Spine P2P IPs |
| `underlay_ibgp` | iBGP | own ASN | MLAG peer via VLAN 4091 |
| `evpn` | eBGP | spine ASN | Spine loopback0 IPs |

**Spine peer groups:**

| Peer group | Type | Neighbors |
|------------|------|-----------|
| `evpn` | eBGP | All leaf loopback0 IPs (each with its own remote-as) |

Spine underlay neighbors are configured individually (no peer-group) since each leaf has a different ASN.

### 7.5 Address families

| AFI | Activated on | Networks advertised |
|-----|-------------|---------------------|
| IPv4 unicast | underlay, underlay_ibgp | Loopback0/32, Loopback1/32 |
| EVPN | evpn | (routes from VLAN/VRF config) |

---

## 8. MLAG standards

| Parameter | Value |
|-----------|-------|
| Domain ID | `{site}-{zone}-pair{NN}` (e.g., `pa-dc-pair01`) |
| Peer-link interface | Port-Channel999 |
| Peer-link VLAN | 4090 (IP: /31 from MLAG peer pool) |
| iBGP VLAN | 4091 (IP: /31 from MLAG iBGP pool, MTU 9214) |
| Peer VLAN autostate | Disabled (`no autostate`) |
| Dual-primary detection | Enabled (delay 10, errdisable all-interfaces) |
| Heartbeat | Via Management0 (VRF mgmt) |
| Virtual MAC | `c001.cafe.babe` (fabric-wide anycast gateway) |

### 8.1 Primary/secondary assignment
- **Odd-numbered leaf** (LEAF-01, LEAF-03, LEAF-05, LEAF-07): lower IP on MLAG VLANs (e.g., x.x.x.0/31)
- **Even-numbered leaf** (LEAF-02, LEAF-04, LEAF-06, LEAF-08): higher IP (e.g., x.x.x.1/31)

---

## 9. VXLAN standards

### 9.1 VTEP interface
- Interface: `Vxlan1` on every leaf
- Source interface: `Loopback1` (shared IP within MLAG pair)
- UDP port: `4789`
- Learning: `vxlan learn-restrict any` (EVPN-controlled)

### 9.2 VNI allocation

| Type | NumberPool name | Range | Usage | Identifier pattern |
|------|----------------|-------|-------|--------------------|
| L2 VNI | `l2-vni-pool` | 100001–199999 | One VNI per extended VLAN (EVPN Type-2) | `l2vni-{site}-{zone}-vlan{NNNN}` |
| L3 VNI | `l3-vni-pool` | 200001–299999 | One VNI per VRF (EVPN Type-5) | `l3vni-{site}-{zone}-{vrf_name}` |

VNIs are allocated from `CoreNumberPool` with deterministic identifiers for idempotent sync.

### 9.3 Route distinguisher and route target

| Service type | RD format | RT format |
|-------------|-----------|-----------|
| L2 VXLAN (per VLAN) | `{ASN}:{VNI}` | `{VLAN_ID}:{VNI}` (import/export) |
| L3 VXLAN (per VRF) | `{Loopback0_IP}:{L3_VNI}` | `{L3_VNI}:{L3_VNI}` (import/export evpn) |

---

## 10. Global parameters

| Parameter | Value | Notes |
|-----------|-------|-------|
| Underlay MTU | 9214 | All P2P and iBGP links |
| Anycast gateway MAC | `c001.cafe.babe` | `ip virtual-router mac-address` |
| Routing model | `multi-agent` | `service routing protocols model multi-agent` |
| Spanning-tree | Disabled on VLAN 4090, 4091 | MLAG VLANs only |
| LLDP | Management0 | `lldp management-address Management0` |
| gNMI | Enabled | `management api gnmi` with `provider eos-native` |

---

## 11. Out of scope (for now)

- **Access switches** — hosts connect directly to leafs
- **Multi-fabric / DCI** — single fabric per site
- **IPv6 underlay** — IPv4 only
- **BFD** — not configured in initial POC
- **Route-maps / prefix-lists** — no filtering in the underlay
- **More than 4 spines** — capped for small DC scope
- **Non-Arista platforms** — EOS only