This is always true. You need to design your network for ISP's speed.
We are still in disagreement (but I now have time for a fuller response).
If we agree to be constrained by what is available financially for most users, take into consideration general users 'ability' in configuring networks and the wide range of ISP speeds offered over the world that can reach and exceed 1Gbps, can we agree that 1GB LAN equipment is our minimum and maximum 'base' equipment for 99.99% of home networks (not to mention most business networks too)? Considering that 10GB LAN solutions are at least 20x the cost currently?
If we do, and that is the premise of my previous posts assuming a 1Gbps ISP connection and a consumer router, then your statement is
not always true. Specifically, it does not mean "If your internet traffic is slowing down your internal network you have a bad design or bad hardware".
Consider the following which I consider normal for most home (and even some small business) networks:
- More than 4 wired users in the network (but usually about 20 and less than 100).
- At least one wired user downloading (multiple) files through our almost 1Gbps ISP connection almost 'always' during peak network times.
- More than one user accessing another computer (or NAS) for media (data) consumption.
- More than one user accessing a NAS concurrently for automatic backup purposes.
- More than one identifiable group of devices that interact frequently with each other and should therefore be on their own separate switch.
With almost any combination of the above scenarios and a not that uncommon 100Mbps to 1Gbps ISP connection, ganging switches when the option of connecting to the router itself is a possibility is a poor choice for overall network performance.
Many times I have greatly improved the network performance of my customers by simply fully utilizing the ports available on the router and, with the more complicated networks, adding a switch for each available router LAN port. Getting rid of the internal LAN bottlenecks does not always mean spending more dollars (for 10GB LAN equipment, for example). Nor does having ISP bottlenecks necessarily indicate a case of bad hardware or hardware design choices (while still being constrained by our wallets).
As I already said; taking advantage of the built in switch of almost all home routers is the cheapest way to design a network for maximum sustained speeds. And the way to that goal is to mimic the physical network layout as closely as possible with the way the data normally flows on it.
This is what will ensure that the network will remain as fast and as responsive as possible even at maximum load.
I have no doubt that at the absolute highest level of network design, your statement is correct. However, we are talking here about an existing $65 router and $49 switch and adding a $20 switch to the mix.