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Cisco DCCOR (350-601) study materials
Cisco DCCOR (350-601) study resources

Cisco DCCOR (350-601): Network

Cisco DCCOR (350-601) · Work through your exam, one topic at a time.

All guide sections

Network

The Network domain carries roughly a quarter of 350-601. It tests whether you can build the Nexus underlay and overlay and predict what happens when a peer-link, VTEP, or site link fails, covering VXLAN BGP EVPN, vPC, OTV, ACI policy, and forwarding details.

VXLAN BGP EVPN

VXLAN puts the original Ethernet frame inside UDP (destination port 4789) with a 24-bit VNI, so one physical network carries up to 16 million segments. The VTEP lives on an NVE interface; the underlay only needs IP reachability between VTEP loopbacks, usually a routed spine with BGP. EVPN supplies the control plane instead of flood-and-learn:

  • Type 1, Ethernet Auto-Discovery, used for multihoming and aliasing
  • Type 2, MAC/IP advertisement, which installs host reachability
  • Type 3, Inclusive Multicast Ethernet Tag, which builds BUM replication lists
  • Type 5, IP prefix, used for symmetric L3 routing

vPC

Two Nexus switches form a vPC domain. The peer-link carries control-plane synchronisation, orphan-port traffic, and any flow that must cross to the other peer; the peer-keepalive must run over a separate path in a separate VRF. Both peers forward, so vPC is active/active, not standby. If the peer-link fails and keepalive stays up, the secondary suspends its vPC member ports to prevent a split-brain.

OTV

OTV extends Layer 2 between sites with MAC-in-IP over UDP 4900. It uses a join interface (IP underlay) and an overlay interface, and it does not forward BPDUs, so each site keeps its own STP domain.

ACI

ACI is declarative: tenants hold VRFs, bridge domains, and EPGs; contracts with subjects and filters allow traffic between EPGs; APIC programs the spine and leaf nodes.

Worked example

A host behind a VTEP sends a 1500-byte frame. Overhead is inner Ethernet 14 + VXLAN 8 + UDP 8 + outer IP 20 = 50 bytes, so the wire packet is 1550 bytes. With a 1500-byte underlay MTU it drops or fragments; the answer is jumbo MTU (typically 9216) on the underlay, or a smaller host MTU.

Traps

  • Mixing up Type 2 and Type 3 EVPN routes.
  • Treating the peer-keepalive as optional or putting it on the peer-link.
  • Assuming OTV passes STP; it filters BPDUs.
  • Reversing ACI contract provider and consumer direction.