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For networks I understand we set a netmask on each computer to let it know what IPs it can talk to without going through the router - IPs on the same subnet can talk directly to each other and do not have to go through a router/switch. However, in today's home networks (and I suspect corporate networks as well) every computer is connected to a router/switch (at the low cost of today's hardware I doubt there it much of a market for wired repeaters/hubs). This seems to obviate the need for a subnet mask and subnetting.

Considering that in most modern home architectures every computer goes through the router, even to talk to computers on the same network, is there any reason for me to subnet a home network?

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It depends on the nature of your home network and how it's used. Are you just "consuming" resources from the Internet? Do you have an "experimental or test" network? Do you offer services back to the Internet via a server? Ultimately - Is there a need to segregate devices by network?

For example, in my "home" network, I have three subnets. I have the regular network - the network to which my girlfriend's PC connects for example. And the one my friends access via their tablet, laptop, or phone, when they come over to visit.

And then I have "my" network, which is for me screwing around and doing things with various flavors of Linux and Windows builds.

And I run an "external" network which has a mumble server, a game server, and occasionally a honeypot (since I like to see what it can catch... - ha!).

Is my infrastructure typical? No, but it's not that unusual either.

In the future (perhaps not immediate - but down the road nonetheless) as more devices in the house become IP connected, QoS issues will likely start to arise. Managing by network (the fridge, microwave, security system, garage opener, and coffee maker go in A, my tablet, laptop, PC, and watch go in B, my TV, game console, security camera, and web server go into C, etc).

It's (usually) easier to manage devices by network than by individual IP. (For example, my devices get priority when downloading something rather than my girlfriend's.... SSHHH).

Then there's the question of IPv4 w/NAT vs the imminently promised arrival of IPv6. If and when IPv6 begins to significantly affect the consumer market (in terms of endpoints), subnetting will be absolutely required. You're evaluating the home environment based on the assumption it always seems like a private 192.168.0/24 environment.

If IPv6 begins to touch consumer endpoints, that isn't necessarily guaranteed. Combine that with the likely need to mix with IPv4 devices, and I could easily see "subnetting" being required. (Of course, almost every consumer router would have to be thrown away and replaced with something new anyway.)

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+1 great answer, hope the GF does not find it! –  Moab Sep 26 '12 at 1:17
The question is also good. +1 to both) –  Serge Sep 26 '12 at 2:08

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