In a medium-sized enterprise network, let's say you have a pair of datacenter switches, a pair of distribution switches, a pair of internal core routers, a pair of firewalls, and a pair of edge routers running BGP connected to the Internet.
When designing physical interconnects between those devices, what are pros and cons of connecting these devices (such as core routers to firewalls, or firewalls to edge routers) directly vs connecting them all only to switches (and using VLANs to facilitate communication)?
In both cases proper link aggregation is set up (each device in a pair to both other devices).
