Enterprise network architecture: who does what, and why there
Every mechanism has a step-by-step animation, the configuration explained line by line and exam notes. Where a parameter changes the outcome, you get a simulator in which you change it yourself.
TL;DR
An enterprise network is split by role: access connects the users and enforces edge security, distribution is the L2/L3 boundary with the redundant gateway, policies and summarization, and the core only routes fast between blocks. When the campus is small, distribution and core sit on the same pair (two tiers); with several buildings, a separate core avoids the mesh of links. The access block can be built with classic STP, loop-free, routed down to access or with two chassis joined together (StackWise Virtual, vPC). The data center uses spine-leaf with VXLAN EVPN, the modern campus SD-Access (LISP + VXLAN + SGT), the WAN SD-WAN with SLA-based routing, and wireless chooses where the CAPWAP tunnel terminates. Availability comes from a tuned FHRP, tracking, SSO/NSF and BFD; the cloud adds new blocks (IaaS) and requires local breakout to SaaS.
How to read the notes: red = critical for the exam, green = theory, blue = numbers, yellow = pitfalls, cyan = differences between platforms, Cisco products and standards. In the animations, the configuration lines used at the current step are highlighted automatically; the ← → arrows change the step when the animation is selected.
The analogy, in short
Think of a county's road network: neighbourhood streets with doormen at the gates (access), county roads with roundabouts and signs that decide where you exit (distribution) and the motorway without traffic lights that links the towns (the core). In a small town the same road does everything; with several towns, you build the motorway so you don't link every town to every other.
The model holds up to §6. From §7 onwards (sealed containers, the population registry, the transport dispatch centre, the buses, the warehouses in another county), the analogy is stretched and has limits; see the full analogy in §15.