Data Center Switching and Fabric Technologies
Domain 2 - Data Center Switching and Fabric Technologies
This domain tests the Layer 2 and overlay building blocks used in Juniper data center fabrics: MC-LAG, EVPN multihoming (ESI-LAG), VXLAN, EVPN, Virtual Chassis, and the QFX switching portfolio. The exam expects you to choose the right multihoming mechanism and explain data-plane and control-plane behavior.
Core rules
- MC-LAG provides active-active server multihoming using ICCP between peer switches; it is a Layer 2 access solution and does not by itself provide a routed fabric overlay.
- EVPN multihoming uses Ethernet Segment Identifiers (ESIs). The same ESI is configured on both leaf switches for a dual-homed server; EVPN type-1 and type-4 routes coordinate DF election and aliasing.
- VXLAN encapsulates Layer 2 frames in UDP; VNIs identify segments. The outer header adds 50 bytes (14 Ethernet + 20 IP + 8 UDP + 8 VXLAN), so underlay MTU must be at least 1550 for 1500-byte payloads, preferably 9000 for jumbo.
- EVPN is the control plane: MAC/IP advertisements, ARP suppression, and anycast gateway reduce flooding and stretch Layer 2 cleanly across the fabric.
- Virtual Chassis is a single logical switch for small pods; it is not a substitute for a leaf-spine fabric at scale.
Worked example
Two QFX leaves connect to one dual-homed server. Configure ESI 00:11:22:33:44:55:66:77:88:99 on the server-facing AE interface on both leaves, with LACP. Both leaves advertise EVPN type-4 ES routes; DF election selects one leaf for BUM forwarding per VLAN, while type-1 per-EVI routes support aliasing. The server sees one LAG. No spanning tree blocking occurs because EVPN multihoming handles loop prevention.
Traps
- Confusing MC-LAG with ESI-LAG: MC-LAG uses ICCP; ESI-LAG uses EVPN.
- Forgetting MTU on underlay links.
- Mismatched VLAN-to-VNI mappings on two leaves.
- Expecting ARP suppression to work without EVPN MAC/IP routes.