Can I make a separate, secondary WiFi network?
June 29, 2015 12:44 PM   Subscribe

I would like to figure out how to make a wireless network inside my house that doesn't interfere/interact with my regular cable modem/wifi. Details to follow ...

I have standard cable company Internet at my house, plenty robust enough for Netflix and anything else I might do, and it all runs on the cable modem/WiFi router that Comcast installed for me. No complaints at all, I'm perfectly happy with the setup.

I also have several older Macbooks/iMacs, all of which have wireless cards that are of a slower variety than my current setup.

I'd like to make a network of just those machines to talk to each other inside the house only, say for file sharing and printer sharing and music, etc, but I want to have that network be completely separate from my regular Internet WiFi. Because a network operates at the speed of the slowest thing attached to it, right? So if I put an old, slow Macbook on my 2015-speed WiFi it would slow everything in the whole house down, right?

a) Is there some reason I don't know of that makes this a bad idea, and b) How would I do this, or what kind of things do I need to be asking Google to dig up instructions? I don't know how to search for this ...
posted by mccxxiii to Technology (8 answers total) 6 users marked this as a favorite
Quick clarifying question: should the MacBooks / iMacs be able to reach the Internet through this new WiFi network?
posted by Tehhund at 12:45 PM on June 29, 2015

You could do two different variants of the same idea:

Buy a second wireless router.
Give it a different name than your current wireless network.
Configure it on a different channel (1, 6, or 11 if you are in the US or Canada).

Here's where the variance happens:

If you want wireless clients on that second network to have access to the Internet, set the "WAN" and "DHCP" settings on the new router to "disabled." Connect an Ethernet cable from a LAN port on the new wireless router to a LAN port on the existing wireless router. Though this mechanism, wireless clients on the new wireless router will still be able to access the Internet but will do so using the older, slower method of encoding data over the air.

If you do not want wireless clients on the second network to have access to the Internet, do nothing. They will be able to talk to each other but not the outside world.

Now, a technical detail: Your question of "everything on the network operates at the speed of the slowest device, right?" The answer is "no" for Ethernet (wired) and "kinda" for wireless. In wireless compatibility modes (to allow older wireless cards and newer wireless cards to work with the same wireless router), the maximum realistic data rate for the fastest device on the network is reduced by between 10 to 20 percent.

If you have an year-old router and modern devices--you do--coexisting with much, much older devices (a 2005 Apple laptop?), you still won't have a problem as long as the Internet service you pay for is under 400Mbps (you have Comcast, so the fastest you can buy in any market, other than a handful of test markets, is 500Mbps). You will be limited more by interference on the 2.4GHz band that wireless routers use than you will by the coexistence of older and newer devices on the same router.
posted by fireoyster at 1:02 PM on June 29, 2015 [4 favorites]

What fireoyster said - in real world terms, the speed of the wifi should not be degraded by placing a slower machine on it, no. If you have an 802.11g device on the network and the router can also do 802.11n, then your 802.11n devices will not noticably suffer from being on this setup.

The only theoretical bottleneck in your network is that if you're using an older machine as a file server, your performance is limited by that machine's processor speed (which really has nothing to do with your wifi speeds) but that's not likely to be an issue in the scenario you're describing. For a few home users, you should be fine by just putting everything on the modem you already have.
posted by randomkeystrike at 1:07 PM on June 29, 2015 [1 favorite]

Yeah I think your premise is flawed (the slowest member should not degrade the network speed)
posted by RustyBrooks at 1:43 PM on June 29, 2015

> So if I put an old, slow Macbook on my 2015-speed WiFi it would slow everything
> in the whole house down, right?

Short answer: Yes, big-time, if the old device is 802.11b. No, not really if it's 802.11g.

A more detailed answer (with explanations of *why* that's the answer) can be found in the Beginner's Guide to Networking.

Good setup advice upthread. Clarification: "give it [the new network] a different name" means specifically give it a different ESSID. (Some routers have a setting called something like "name" that's just a hostname or the like. The ESSID is what needs to be different.)

In a "greenfield" deployment, I like to use simultaneous dual-band APs, run 802.11n only on 5GHz and mixed-mode on 2.4GHz. I mention that because you might want to consider paying a few extra bucks to future-proof, should you someday ditch the Comcast CPE and get a cable modem with no built-in WiFi.
posted by sourcequench at 1:51 PM on June 29, 2015 [3 favorites]

It's pretty easy in most cases to get your Wifi router to radiate 2 wifi hotspots, one in the 2.4GHz range (which all of your old devices will support and one in the 5GHz range, which you can reserve for your new devices. They'll either have different names or two variations on a common name.

In both cases, take the opportunity to get a wifi-scanning app to see what channels (== frequencies) your neighbors' wifi is on, assuming you have neighbors within 500 feet or so). Pick a channel that's 3-4 (or more; think of your signal-- and everyone else's-- as being 4 channels wide) away from your neighbor in the 5GHz band, or use 1,6,11 (as above-- up to 13 if you're not in North America) in the 2.4GHz band. All your neighbors should also be on 1,6, or 11, and if you're thinking of picking something interference, please trust a network engineer that this increases interference for you and the neighbors rather than decreasing it-- it has to do with how networks share the channel.

Most likely your router can already do this; if not, you can switch your Wi-Fi load to a bog-standard off-the-shelf wireless router and turn off the cable modem.

Okay, looks like sourcequench has beaten me to this, so call this my seconding of that advice.
posted by Sunburnt at 2:02 PM on June 29, 2015

So if I put an old, slow Macbook on my 2015-speed WiFi it would slow everything in the whole house down, right?

As others have said, no.

Even the very first Macbooks and Macbook Pros from 2006 can support 802.11n networking, which is still the standard for the kind of conventional 2.4Ghz Wi-Fi your cable-provided access point likely supports. It will not limit the wireless speeds of other, newer devices.

As has previously been mentioned, devices that are much older - 802.11b devices - can limit network speed. But even the old Aluminum Powerbooks from the early aughts used 802.11g-compatible wireless cards. You probably don't have any 802.11b devices.

If you don't need to separate networks for purposes of security, you probably shouldn't bother. Trying to do file, print and music sharing on two different 2.4Ghz networks is far more trouble than it's worth - there's a tremendous benefit in terms of both compatibility and maintenance having all of your home devices being able to talk to each other on a single network.
posted by eschatfische at 3:26 PM on June 29, 2015 [1 favorite]

It may be easier for you to buy Mac-compatible USB WiFi adapters and "upgrade" your Macs so everybody use the same network. The "n" adapters are cheap, the trick is finding ones with Mac support, if you have pretty old Macs. No need to upgrade them to AC. Pretty sure your cable modem's WiFi is "N".
posted by kschang at 3:14 AM on June 30, 2015

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