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JNCIP-DC study materials
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JNCIP-DC: Data Center Switching and Fabric Technologies

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

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Data Center Switching and Fabric Technologies

This domain tests the Layer 2 and multihoming mechanics underneath the overlay: VLAN and trunk behavior, LACP, MC-LAG, EVPN ESI multihoming, storm control, and VTEP data-plane function.

Layer 2 fundamentals

  • Access ports carry untagged frames into one VLAN; trunk ports carry tagged frames. A native VLAN or native-vlan-id mismatch silently black-holes traffic while interfaces stay up.
  • IRB interfaces provide the Layer 3 gateway for a VLAN. In EVPN designs, use a shared anycast MAC and IP on every leaf so a host keeps its gateway after migration.
  • RSTP or VSTP is still required for non-EVPN Layer 2 loops. Do not run two loop-prevention mechanisms (STP plus ESI) on the same segment.

Multihoming

  • MC-LAG: two QFX switches form a multichassis bundle with an inter-chassis link and ICCP. There is one shared LACP system ID, active-active forwarding, and per-protocol active/standby roles.
  • ESI-LAG (EVPN multihoming): each leaf keeps its own control plane. Both leaves are configured with the same ESI value, the same LACP system ID, and the same ESI mode (all-active). EVPN Type-1 and Type-4 routes coordinate them, and designated forwarder election selects who forwards BUM traffic per segment.

Worked example

A server is dual-homed to leaf1 and leaf2 in an EVPN fabric. On both leaves, configure ae0 with LACP, the same system ID (00:00:00:00:00:01), and the same ESI under switch-options ... esi, mode all-active. Both leaves advertise a Type-4 route per ESI and Type-1 A-D routes per ESI; Type-2 MAC routes for the server carry the ESI. A remote leaf receiving traffic for the server MAC sees the ESI and programs an aliased next hop, so both links are used. Verify with show evpn ethernet-segment (DF state) and show lacp interfaces ae0 (members up on both leaves).

Traps

  • Mismatched ESI or LACP system ID, which splits one logical segment into two and causes MAC flapping.
  • Applying the ESI to a physical access port instead of the aggregated Ethernet interface.
  • Forgetting to allow the tenant VLAN on the ICL/trunk.
  • Storm-control thresholds set too low on vMotion or backup VLANs, dropping legitimate bursts.