Macfilter: How can I use ethernet and wifi at the same time on my Macs?
December 8, 2007 5:52 PM   Subscribe

Is it possible to connect two macs via ethernet (to share files back and forth on their wired LAN), but both be connected to the internet wirelessly at the same time using airport? (an airport extreme is connected to DSL on the lower level of the apartment). If so, how?

More information if necessary: (recently purchased Airport Extreme basestation connected to DSL; G5 with Tiger; iMac-intel with Tiger). I'd like to ethernet the two Macs so they're networked to share files, etc, but have them be able to use the remote Airport extreme to connect to the web.
posted by lonemantis to Computers & Internet (19 answers total) 4 users marked this as a favorite
Yes. You set up one of the macs to pick up the internet connection from the Airport, and then share it with the other mac via ethernet.

If you are using Leopard, go to the Mac you want to connect to the Airport and open the Sharing preference pane in system preferences . Turn on 'Internet Sharing' and set 'Share your connection from' to be 'Airport' and set 'to computers using' to be 'Ethernet'.

Go to the other computer and set it to connect via DHCP on Ethernet and you're done.
posted by unSane at 6:04 PM on December 8, 2007

I think you can also be connected via Ethernet and Airport at the same time but you have to be careful to make sure the subnet IP addresses don't collide.

EG set you Airport IP addresses to be and your Ethernet IP addresses to be
posted by unSane at 6:05 PM on December 8, 2007 [1 favorite]

unSane has it. Just give the different subnets. If you go under System Preferences, Network, Airport, and then TCP/IP, what values do you have for IP Address and Subnet Mask?
posted by sbutler at 6:14 PM on December 8, 2007

Response by poster: Here are my IP addresses for Airport (I am looking in the Sys Pref on the G5): IP:; subnet mask: (the configure IPv4 is "Using DHCP") Is there any other information you guys / gals need? I am pretty proficient with Macs but networking is totally Greek to me... thanks for any continued help you can provide.
posted by lonemantis at 6:21 PM on December 8, 2007

If you're just putting a patch lead between the two Macs, you don't really need to mess around with setting IP addresses for the wired network as it'll make up its own IP addresses that don't conflict with the wireless (actually, it'll do this even if they're on a wired network).

I have my house working in the same way, with two computers connected through a wired router but also using wireless. They cleverly default to using the wired connection between each other, without me doing anything, and use the wireless for everything else. It's all seamless.
posted by wackybrit at 6:22 PM on December 8, 2007

Response by poster: I forgot to mention that the two computers are NOT yet connected via the ethernet cable. Would the IP addresses, etc, change if I just plugged in the ethernet cable between them?
posted by lonemantis at 6:22 PM on December 8, 2007

Note that my suggestion will only likely work if the wireless hub is NOT on the wired network. If it's not, then it won't be providing DHCP to the wired network. So just plug the wires in, and it'll just work, no settings necessary.
posted by wackybrit at 6:23 PM on December 8, 2007

Response by poster: Wackybrit, the wireless hub is NOT wired to any of the macs on the network. Here's the diagram: WALL<>phone(DSL)<>Airport Extreme |||||||||no wires||||||||| G5|||||||| no wires |||||| Macintel iMac
posted by lonemantis at 6:25 PM on December 8, 2007

Response by poster: Wackybrit, so after taking a look at my "diagram" LOL.... do you think just plugging in the ethernet cable between the two macs would work? (so that direct file sharing would be through the ethernet cable, but the internet connection via wireless would still work? If so, what if another computer (wireless) is nearby, can the airport wireless still connect to it? So that there's a mix of wired and wireless computers without my having to fiddle with settings?
posted by lonemantis at 6:27 PM on December 8, 2007

Yes. OS X is designed to self provide IP addresses on networks where there are no DHCP servers. As the "wired" network is separate from the wireless one, even though you can access both at once, if you connect the two Macs they should self-assign IP addresses. If you then used, say, afp://your-machine-name.local to connect between the machines (or Leopard's self detecting sharing, I guess) then it'll use the best network for the job.

The reason I know this is that I did exactly this myself and then got 40MB/sec transfer rates between the two machines, which I know the wireless network can't possibly do :) That said, I have noticed that if you have some file sharing going on BEFORE you plug the ethernet cables in, it will remain on the wireless until you disconnect that file sharing then re-establish it. Basically, connectivity will remain on whatever interface it started on.

What the other commenters suggest here, however, is technically correct, but just doesn't seem necessary under OS X. It's good advice if you were networking, say, an OS X machine to a Linux or Windows machine, however.
posted by wackybrit at 6:42 PM on December 8, 2007

Just Plugging In The Cables has also Just Worked on Ubuntu for at least the last couple of releases. It works for Windows too, even though you will see complaints about the interface having "limited connectivity". It even works to connect machines with disparate operating systems to each other, because there's a standard that says that machines are allowed to self-assign IP addresses in the 169.254.x.x range if they find cables plugged in but no DHCP server available.
posted by flabdablet at 6:53 PM on December 8, 2007 [1 favorite]

Yeah, just plug in the cables and see what happens. Hopefully the Macs will find each other via Bonjour and Bob's your uncle.
posted by unSane at 7:00 PM on December 8, 2007

I love the phrase "Bob's your uncle"... I just had to say that..

And, what folks are saying should work... os x is smart like that...
posted by HuronBob at 7:19 PM on December 8, 2007

Response by poster: Thanks for all your help everyone... I may need some more:

If I wanted to know what method the two macs were "finding" each other by (wireless or ethernet cable), without actually sharing a file, is there anyway to tell?

Here's what I did: I disabled file sharing on both macs, (airport still active), then connected an ethernet cable, then enabled file sharing on both macs, and am currently swapping files, but it doesn't seem any faster than when they were wifi networked... so, I even checked in activity monitor and the highest network usage number was around 716KB/sec.... a far cry from 40MB/sec. Maybe I'm just missing something.
posted by lonemantis at 8:06 PM on December 8, 2007

If you disable wireless, put a wire directly between the two machines, and you're getting 716KB/sec on a *large* file then there are problems as you should be getting a direct 1Gbps link (not sure if the G5 had gigabit ethernet, but it'll be at least 100Mbps / approx 12.5MB/sec). If you're only getting 716KB/sec but you're copying 1000s of tiny files, that's not so surprising.
posted by wackybrit at 8:52 PM on December 8, 2007

THe first thing to check is that they can really see each other via the wired connection. Turn off the Airport on both, plug in the Ethernet, give it a few minutes, and then make sure they can see each other and transfer files. If they can, then turn the Airports back on and you should be golden.

Over the long term, you may have issues with connectivity. The autoconfiguration process on a wired link is fairly slow when you don't have a DHCP server. This means that the Macs will usually bring up their Airport before they bring up their Ethernet connections, and I suspect they'll use whichever method they saw first to talk to each other.

You can avoid this issue by assigning static IPs on the Ethernet. The 169.254.X.X range is fine. Use, say, on one, and on the other. That way, they will waste no time trying to find a DHCP server that isn't there. Your Ethernet should always come up first, since wireless takes a few seconds to negotiate, and thus you should get the high speed connection by default.

If you want to REALLY be sure, you'd connect to fileshares by IP address, but I think you have to get into the Terminal to do that. Most likely, assigning static IP addresses will work, and it's very easy.

One last thing: if the Macs won't connect via Ethernet, you might need a crossover cable. Most modern machines are smart enough now that they don't require crossovers anymore. If at least one of your Macs is recent, you should be fine. But if it won't connect, try either a crossover cable, or two regular cables plugged into a hub/switch.
posted by Malor at 8:58 PM on December 8, 2007

Response by poster: Thanks everyone for your help!!! So far it seems to be working. I disabled Airport from both macs... connected the ethernet cable, went into Sys Prefs, and Confgure iPV4 "using DHCP with manual address" on both macs (one with and the other with, clicked apply to both macs. Waited a bit.

I then chose GO>connect to server from my G5, and typed in the afp://machinename.local to connect to my wife's iMac. Viola! but the true test was transferring a 1.2GB file, which got me up to around 40MB/sec!!!

I then enabled Airport, and we're both on the internet, but file sharing seems to go through ethernet! Wonderful!!!

Thank you so much!

I just hope that these connections and settings will remain after one or both computers restart after shutdown.
posted by lonemantis at 8:53 AM on December 9, 2007

Hi, I have a slightly different setting, with which the above suggestions don't work :-(

I have a WiFi network to which a MacMini (with Leopard) is connected. An ethernet NAS disk is connected directly to the MacMini via ethernet. The shares of the NAS disk are correctly mounted on the MacMini.

My goal would be to be able to see the NAS shares also from other Macs connected to the WiFi.
This is roughly the architecture:

<> MacMini <> NAS-disk
<> OtherMac

The NAS-disk is configured to advertise itself via bonjour and appletalk: in fact, when I connect the NAS-disk directly to the WiFiRouter via ethernet, both the MacMini and the OtherMac see the shares of the NAS-disk.

However, when the NAS-disk is connected as above to the MacMini, then only the MacMini sees its shares. I tried to put the shares of the NAS-disk as shared folders in the File Sharing part of the Sharing panel, but apparently they are not accepted (I can not drag them there, nor are they selectable from a file browser window). I also tried to do an Internet Sharing from Airport to Ethernet as suggested her, but to no avail.

What should I do?

posted by franconi at 10:33 AM on April 2, 2008

Sorry, the above architecture is not rendered correctly; let me try again.

~~~~~~~~~~~~~~~~~~~~~~ MacMini ------ethernet------ NAS-disk
~~~~~~~~~~~~~~~~~~~~~~ OtherMac
posted by franconi at 10:35 AM on April 2, 2008

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