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How to Build a Juniper EVPN-VXLAN Fabric: BGP EVPN Overlay (Part 2)

tania andrew Suresh Thapa
| 20 Mar | 615 views
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How to Build a Juniper EVPN-VXLAN Fabric: BGP EVPN Overlay (Part 2)

n Part 1, we built the underlay network that provides IP reachability across the fabric.

Now in Part 2, we move to the control plane of the overlay — BGP EVPN, which is the brain of the VXLAN fabric.

This is where:

  • MAC addresses are learned
  • VXLAN tunnels are controlled
  • Tenant networks are extended across the fabric

 

What is BGP EVPN Overlay?

BGP EVPN replaces traditional flooding-based learning with a control-plane driven approach.

Instead of:
    Flood & Learn
We use:
    BGP to distribute MAC/IP information

 

Overlay Design in This Lab

  • Spine → Acts as Route Reflector (RR)
  • Leafs → EVPN clients (VTEPs)
  • Peering → eBGP (recommended for scalability)
  • Source IP → Loopback (lo0)

 

Why Use eBGP for EVPN?

eBGP is widely used in modern fabrics because:

  • Simple design (no IGP dependency for overlay)
  • Better scalability
  • Clear ASN separation per leaf
  • Faster convergence

 

Spine Configuration (Route Reflector)

The spine acts as a central control-plane node that reflects EVPN routes between leaf switches.

 

Explanation

  • type external
    → Using eBGP between spine and leaf
  • family evpn signaling
    → Enables EVPN route exchange (MAC/IP routes)
  • multihop ttl 5
    → Required because loopback interfaces are used
  • no-nexthop-change
    → Preserves the original VTEP IP (very important for VXLAN)
  • local-address should be the loopback address ex-10.0.0.1
    → Spine loopback used for BGP peering
  • multipath
    → Enables ECMP for load balancing

 

Key Design Concept

  • Each leaf has its own ASN
  • Spine is in a different ASN
  • Spine acts as a Route Reflector-like node in eBGP design

👉 This avoids full mesh between leaf switches.

 

How Route Reflection Works Here

  1. Leaf sends EVPN routes to Spine
  2. Spine reflects routes to all other Leafs
  3. Leafs learn MAC/IP of remote endpoints

 

Topology

VXLAN Diagram

 

Step 1: Configure BGP EVPN Overlay Group

 

Spine01

# Configure the BGP Overlay Group
set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY multihop no-nexthop-change
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.1
set protocols bgp group EVPN-OVERLAY multipath

 

Step 2: Configure Leaf Neighbors

Each leaf peers with the spine using its loopback IP.

# Peer with Leaf 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.11 peer-as 65101
# Peer with Leaf 02
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.12 peer-as 65102
# Peer with Leaf 03
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.13 peer-as 65101
# Peer with Leaf 04
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.14 peer-as 65102
# Peer with Leaf 05
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.15 peer-as 65102

 

 

Spine02

# Configure the BGP Overlay Group
set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY multihop no-nexthop-change
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.2
set protocols bgp group EVPN-OVERLAY multipath

 

Configure Leaf Neighbors

# Peer with Leaf 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.11 peer-as 65101
# Peer with Leaf 02
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.12 peer-as 65102
# Peer with Leaf 03
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.13 peer-as 65103
# Peer with Leaf 04
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.14 peer-as 65104
# Peer with Leaf 05
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.15 peer-as 65105

 

 

Leaf01

# Configure the BGP Overlay Group
set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.11

 

Configure Spine Neighbors

# Peer with Spine 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.1 peer-as 65000
# Peer with Spine 02 (If you have configured it)
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.2 peer-as 65000

 

 

Leaf02

set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.12

 

Configure Spine Neighbors

# Peer with Spine 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.1 peer-as 65000
# Peer with Spine 02 (If you have configured it)
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.2 peer-as 65000

 

 

Leaf03

# Configure the BGP Overlay Group
set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.13

 

Configure Spine Neighbors

# Peer with Spine 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.1 peer-as 65000
# Peer with Spine 02 (If you have configured it)
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.2 peer-as 65000

 

 

Border-Leaf01

# Configure the BGP Overlay Group
set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.14

 

Configure Spine Neighbors

# Peer with Spine 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.1 peer-as 65000
# Peer with Spine 02 (If you have configured it)
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.2 peer-as 65000

 

 

Border-Leaf02

# Configure the BGP Overlay Group
set protocols bgp group EVPN-OVERLAY type external
set protocols bgp group EVPN-OVERLAY family evpn signaling
set protocols bgp group EVPN-OVERLAY multihop ttl 5
set protocols bgp group EVPN-OVERLAY local-address 10.0.0.15

 

Configure Spine Neighbors

# Peer with Spine 01
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.1 peer-as 65000
# Peer with Spine 02 (If you have configured it)
set protocols bgp group EVPN-OVERLAY neighbor 10.0.0.2 peer-as 65000

 

What Routes Are Exchanged?

BGP EVPN carries:

  • Type 2 → MAC + IP routes (host reachability)
  • Type 5 → IP Prefix routes (for L3 VXLAN)
  • Type 3 → IMET routes (BUM traffic handling)

 

Verification Commands

After configuration, verify the overlay:

show bgp summary
show route table bgp.evpn.0

 

Expected Outcome

  • BGP sessions should be Established
  • EVPN routes should start appearing
  • Leafs should learn remote MAC/IP entries

 

Common Mistakes

❌ Missing family evpn signaling
❌ Wrong loopback IP in local-address
❌ No underlay reachability between loopbacks
❌ Forgetting no-nexthop-change

 

Series Recap

 

Conclusion

The EVPN overlay is the core of a modern data center fabric. By using BGP, we achieve:

  • Scalable MAC learning
  • Efficient traffic forwarding
  • Elimination of flooding
  • Multi-tenant support

This lays the foundation for a fully automated, scalable VXLAN fabric.

Tags:

BGP EVPN Juniper VXLAN

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