Junos EVPN-VXLAN CRB Fabric: Step-by-Step Config

Modern data center fabrics are IP fabrics: BGP-based EVPN signals reachability in the control plane while VXLAN encapsulates frames in the data plane. Juniper's official example walks through a complete centrally routed bridging (CRB) fabric — two QFX spines, four QFX leaves, three VLANs, and full inter-VLAN routing done on the spines via IRB interfaces. This article condenses that configuration into the key building blocks: underlay eBGP, overlay iBGP, IRB gateways, VLAN-to-VNI mapping, and the verification commands that prove the fabric works.

CRB Architecture in a Nutshell

In a CRB design, integrated routing and bridging (IRB) interfaces are defined on the spine devices only — all inter-VLAN routing happens centrally at the spine layer. Leaves perform pure L2 bridging and VXLAN encapsulation. Each VLAN maps to a unique VXLAN Network Identifier (VNI); each IRB interface carries a unique subnet and serves as the default gateway for its VLAN, using a virtual gateway address for redundancy.

Spine 1: Underlay Configuration

• Configure the L3 fabric interfaces and a loopback that serves as the VXLAN source address.
• Enable BGP multipath so all equal-cost paths through the underlay are used.
• Configure a load-balancing policy (per-packet) and a policy to advertise direct/loopback routes into the underlay.

set policy-options policy-statement export-direct term 1 from protocol direct
set policy-options policy-statement export-direct term 1 then accept
set routing-options autonomous-system 65001

Spine 1: Overlay and Access Profile

• Configure an iBGP group for the EVPN address family, peering with the other spine and the leaves.
• Configure VXLAN encapsulation and no-gateway-community for EVPN.
• Define IRB interfaces for VLANs 101/102/103, each with its own subnet and virtual-gateway-address.
• Map VLANs to VNIs (e.g., VLAN 101 → VNI 10101) and set a route target per VNI.

Leaf Configuration

Leaves in a CRB fabric have no IRB interfaces — only L2 functionality:

• eBGP group toward the spines for underlay routing; iBGP group for the EVPN overlay.
• Configure VXLAN encapsulation and how multicast/BUM traffic is replicated.
• Create a virtual-switch routing instance, map VLANs to the same VNIs used on the spines, and set route targets.
• Configure the access interface as a trunk (or untagged access) carrying the server VLAN.

Verification

show route table serverBD.inet.0          # IRB routes present?
show evpn vxlan tunnel                   # VTEP tunnels established
show bgp summary                         # EVPN neighbors up

The sample outputs show the IRB interface routes for all three VLANs in the routing instances and successful ping tests between servers in different VLANs. For design context, compare with our VXLAN MP-BGP EVPN design guide, the HPE Aruba EVPN-VXLAN Fabric Composer article, and 400G spine / 100G leaf link consistency.

原文链接：https://www.juniper.net/documentation/us/en/software/junos/evpn/topics/example/evpn-vxlan-irb-within-data-center.html