Each network (e.g : Switches, Routers, Firewalls) used must have an explanation for the drawings.
Also, at the end , explain:
1) The feasibility of the proposed Network Design (e.g : whether this network diagram is technically viable or not?)
2) Suitability of the proposed Network Design for the given scenario (e.g : Is the proposed Network Design suitable for the given scenario?)
The most important is the drawing/diagram of the network and the explanation for each network used.
