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I often confuse "commercial" routers (which include switching, dhcp, firewall, etc. functionality) with "academic" routers (strictly layer 3). My question can be summed up in the following image:

enter image description here

Are commercial routers (let's say for example a Netgear N600) similar to the left or the right? Also: if I wanted to have multiple subnets on the LAN side, could this be accomplished? (Considering if my router is the left, then I assume not given the "router" really only has 2 ports).

Grant
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Zach
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    AFAIK there is no term 'commercial' router. The term you are looking for is probably **consumer** router, or broadband router. Which usually amounts to a 2 port router with the LAN port connected to an internal switch/hub. If you want multiple networks you probably need to looking at buying better equipment. – Zoredache Nov 19 '13 at 18:20
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    Enterprise grade routers won't pigeon-hole into either of those pics. They are "routers", capable of routing packets between disparate networks. The term gets a lot of crossover nowadays (think Venn Diagram) into the switching world and vice versa. It can involve a WAN but doesn't have to. It can have features that you describe or maybe it doesn't. A Netgear N600 would fall into consumer grade. Comparing it to say a Cisco 7304 would be like saying a Chevy Aveo and a Bugatti Veyron are "similar enough". – TheCleaner Nov 19 '13 at 18:55

2 Answers2

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An IP router is a device that looks at layer 3 information (IP addresses) and decides where to send a given packet based on a routing table -- Usually this means handing it to another router.

A switch is a device that looks at Layer 2 information (MAC addresses) and decides where to send a given ethernet frame (which port), based on a table of which MAC addresses are reachable via which ports.

Your typical "Consumer Router" (Like these Linksys models) usually contains both devices, plus a NAT-capable firewall (and very often a Wireless Access Point).
Your N600 looks like this inside:
enter image description here

A typical Enterprise router is just a router - It may have multiple interfaces, but its purpose is to take packets in on one interface, match them against its routing table, and forward them out one of its other interfaces to continue on its journey.
One or more of those interfaces may be connected to switches or firewalls (either via a cable or through a chassis backplane).

Generally speaking if you want multiple subnets on the LAN side you would need multiple interfaces (or virtual interfaces), or take other steps to make the router aware that multiple subnets reside on the LAN interface (how you do this depends on your router).
You may also use a Layer 3 Switch which is essentially a lobotomized router (a switch that is aware of multiple subnets and will move traffic across networks for you, but isn't usually capable of handling a "WAN" interface).

For more information you should consult your vendor's documentation.

voretaq7
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Logically, a router is a switch that filters on things beyond MAC address. A consumer grade (like the Netgear) has just a switch, the ports are not filtered from each other, and cannot be routed. Now on many, you do have a DMZ option, but I've never really looked into what that provides.

Your subnetting will need to be done by a device that can route between ports.

Ronald Pottol
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