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JNCIS-DC study materials
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JNCIS-DC: Data Center (JNCIS-DC)

JNCIS-DC · Work through your exam, one topic at a time.

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Data Center (JNCIS-DC)

What this domain tests

The Data Center domain of JNCIS-DC tests whether you can explain and apply Juniper's EVPN-VXLAN data center fabric: the IP underlay, the BGP EVPN control plane, VXLAN data-plane encapsulation, and the Junos/Apstra tooling used to deploy it. Questions are scenario-based - you are given a topology or configuration fragment and asked what a device will advertise, install, or forward.

Core rules and concepts

  • The underlay is a routed IP fabric, typically eBGP between leaf and spine, providing loopback-to-loopback reachability. VTEPs are leaf loopback addresses.
  • VXLAN encapsulates Layer 2 frames in UDP with destination port 4789. The VNI is a 24-bit identifier scoped to a bridge domain and is not the same thing as a VLAN ID.
  • BGP EVPN carries reachability: Type 2 = MAC/IP advertisement, Type 3 = inclusive multicast (IMET) for BUM traffic, Type 5 = IP prefix route for symmetric IRB.
  • Route targets control import and export between EVPN instances. Matching RTs are what stretch a VNI across leaves.
  • ESI multihoming lets a host dual-home to two leaves without MC-LAG. The same ESI carried in Type 2 routes signals all-active attachment.
  • Anycast gateway gives every leaf the same distributed IRB MAC and IP, so a VM can move without re-ARPing. It is not VRRP.

Worked example

A leaf learns MAC 00:11:22:33:44:55 on an access interface in VLAN 100, mapped to VNI 10100, and the host also sends an ARP reply with IP 10.10.10.5. The leaf advertises an EVPN Type 2 route containing the MAC, the IP, VNI 10100, and its VTEP loopback as next hop. Reasoning: the MAC alone would be a Type 2 without an IP; the ARP reply lets the leaf include the IP, which remote leaves use to install a /32 host route for proxy ARP and symmetric IRB. A Type 3 route is also sent so BUM traffic from remote leaves reaches this VTEP.

Traps that cost marks

  • Confusing VNI with VLAN ID, or assuming a VNI has significance beyond the fabric.
  • Forgetting that Type 3 handles BUM replication, not unicast MAC learning.
  • Assuming ESI requires LACP; ESI is a BGP attribute, and all-active mode is a separate setting.
  • Mixing up route-target direction: export on the originator, import on the receiver.