# EBGP Data Center Fabric

We want to create EBGP-only leaf-and-spine. The fabric will have two leaves (l1, l2) and two spines (s1, s2).

The only routing protocol running in the network is BGP.

```
module: [ bgp ]
```

The default device type is Arista EOS:

```
defaults:
  device: eos
```

The network topology has four nodes. Each node has a different AS number:

```
nodes:
  s1:
    bgp:
      as: 65000
  s2:
    bgp:
      as: 65001
  l1:
    bgp:
      as: 65100
  l2:
    bgp:
      as: 65101
```

The inter-switch links form a leaf-and-spine fabric:

```
links:
- s1-l1
- s1-l2
- s2-l1
- s2-l2
```

By default, each switch advertises its loopback interface into BGP (there are no stub links in the network topology).

## Resulting Data Structures

Data structures generated by the BGP data transformation module include the list of BGP neighbors. Each node has two EBGP neighbors -- here is the data structure describing S2:

```
- bgp:
    as: 65001
    neighbors:
    - as: 65100
      ipv4: 10.1.0.9
      name: l1
      type: ebgp
    - as: 65101
      ipv4: 10.1.0.13
      name: l2
      type: ebgp
    next_hop_self: true
```

## Resulting Device Configurations

The above topology generates the following BGP-related device configuration for S1 (Arista EOS):

```
router bgp 65000
  neighbor 10.1.0.1 remote-as 65100
  neighbor 10.1.0.1 description l1
!
  neighbor 10.1.0.5 remote-as 65101
  neighbor 10.1.0.5 description l2
!
 address-family ipv4
!
  network 10.0.0.3/32
!
!
  neighbor 10.1.0.1 activate
  neighbor 10.1.0.5 activate
```

This is the BGP configuration for an Arista EOS leaf switch:

```
router bgp 65000
  neighbor 10.0.0.3 remote-as 65000
  neighbor 10.0.0.3 description s1
  neighbor 10.0.0.3 update-source Loopback0
  neighbor 10.0.0.3 next-hop-self
!
  neighbor 10.0.0.4 remote-as 65000
  neighbor 10.0.0.4 description s2
  neighbor 10.0.0.4 update-source Loopback0
  neighbor 10.0.0.4 next-hop-self
!
 address-family ipv4
!
  network 10.0.0.2/32
!
!
  neighbor 10.0.0.3 activate
  neighbor 10.0.0.4 activate
```

## Complete network topology

```
module: [ bgp ]

defaults:
  device: eos

nodes:
  s1:
    bgp:
      as: 65000
  s2:
    bgp:
      as: 65001
  l1:
    bgp:
      as: 65100
  l2:
    bgp:
      as: 65101

links:
- s1-l1
- s1-l2
- s2-l1
- s2-l2
```