1.0 Architecture

What this domain tests

Architecture is the exam domain that asks: can you look at a network design and tell what problem each part solves? Do not study it as product trivia. Study it as control points, failure domains, and tradeoffs.

Domain 1 is 15% of ENCOR. It covers enterprise campus design, high availability, Catalyst SD-WAN, SD-Access, and QoS interpretation. That mix is deliberate. Cisco wants you to understand how modern enterprise networks are built: a physical underlay, an overlay or policy system when useful, and enough operational proof to know whether traffic is actually taking the path you intended.

The mental model

• 2-tier campus means access plus collapsed core/distribution. It is common in small and medium sites.
• 3-tier campus means access, distribution, and core. It buys scale, cleaner failure domains, and simpler growth.
• Fabric means an overlay with centralized identity, segmentation, and endpoint mapping. The underlay still matters.
• Cloud means your WAN, identity, policy, and routing now extend to infrastructure you do not physically own.
• High availability is not one feature. It is redundant paths, redundant devices, fast failure detection, stateful failover, and tested recovery.
• SD-WAN centralizes policy and builds encrypted overlays across multiple transports.
• SD-Access centralizes campus segmentation and endpoint mobility using LISP, VXLAN, and policy.
• QoS is only useful if you can read the policy and the counters. A pretty policy with zero matches does nothing.

Domain 1 map:

Campus L2/L3 ---- FHRP + EtherChannel + STP
      |
      +-- WAN overlay (SD-WAN: OMP control + encrypted data tunnels)
      +-- Campus fabric (SD-Access: LISP + VXLAN + SGT policy)
      +-- Edge QoS (classify -> queue -> verify counters)

Commands worth recognizing

You do not need every command memorized for architecture, but you should know what each command is trying to prove.

show etherchannel summary
show spanning-tree root
show standby brief
show redundancy states
show sdwan control connections
show sdwan omp peers
show sdwan bfd sessions
show lisp instance-id <id> ipv4 map-cache
show cts role-based permissions
show policy-map interface

Lab path

Build this domain in layers. First draw a small campus with two access switches and two distribution switches. Add VLANs, trunks, EtherChannel, and an FHRP gateway. Then draw the same site attached to two WAN transports. Label which device owns management, control, and data plane decisions. Finally, add a QoS policy on the WAN edge and prove which class packets match.

The exam habit you want is simple: read the topology, name the control point, name the failure domain, and name the command that proves the design works.

Pass check

You are ready for Domain 1 when you can explain why a 3-tier campus is not automatically better than a 2-tier campus, why an SD-WAN overlay still depends on the underlay, why SD-Access still needs routing to leave the fabric, and why QoS verification starts with counters instead of configuration beauty.