1.1 Explain the different design principles used in an enterprise network

What to learn

Enterprise design is about making the network predictable. The exam does not reward vague words like scalable or resilient unless you can attach them to an actual design choice.

A clean campus design answers four questions:

• Where do users and endpoints attach?
• Where is Layer 2 allowed to exist?
• Where does Layer 3 routing begin?
• What happens when a link, switch, supervisor, or gateway fails?

2-tier, 3-tier, fabric, and cloud

In a 2-tier campus, access switches connect to a collapsed core/distribution pair. This is simple and fast to operate. The tradeoff is that the collapsed layer does many jobs: routing, policy, aggregation, and WAN or data center handoff.

In a 3-tier campus, access connects to distribution, and distribution connects to core. The core should be boring: fast routing, low latency, no unnecessary policy. The distribution layer is where summarization, default gateways, filtering, and service boundaries usually live.

In a fabric, the physical topology is the underlay. The user experience is delivered by the overlay. Endpoint identity, segmentation, and mobility become more important than VLAN geography.

In cloud-connected designs, the same principles still apply. You still need routing control, segmentation, inspection points, redundancy, and observability. The difference is that part of the network is now a provider service.

High-availability baseline lab

Use this as a small practice build. Two distribution switches provide the default gateway for VLAN 10. Access switches connect with trunks or EtherChannels. The goal is to lose one distribution switch or uplink without losing the user subnet.

vlan 10
 name USERS

interface Port-channel10
 description ACCESS-SW1 dual-uplink
 switchport mode trunk
 switchport trunk allowed vlan 10

interface Vlan10
 description USERS gateway
 ip address 10.10.10.2 255.255.255.0
 standby version 2
 standby 10 ip 10.10.10.1
 standby 10 priority 110
 standby 10 preempt

Verify the design, not just the syntax.

show interfaces trunk
show etherchannel summary
show standby brief
show ip route 10.10.10.0

Exam traps

A redundant-looking diagram can still have one failure point. A switch stack can hide device failure from the access layer, but it is still one operational unit. A fabric does not remove routing; it changes where endpoint reachability is learned. Cloud does not eliminate network design; it punishes sloppy design faster because failures cross ownership boundaries.