Help me troubleshoot a down-home style network.

November 21, 2007 9:20 PM

At my parents for Thanksgiving and I need help troubleshooting family Airport wireless! Three Macs, one IP address...FIGHT!

Last time I was home, I was called in to deal with technical support trying to make routers and the Airport play nice. We got it working, to a degree- the Airport is set up with a manual IP address, as dictated by the ISP. The one computer that is connecting to the internet does so can only do so using the same manual IP address, even though I've got the Airport to distribute addresses. Should I attempt to set up a range of IP addresses from the Airport and set each computer to manually connect to one? Or...what?

posted by 235w103 to computers & internet (13 comments total)

I don't have an Airport handy to check, but ... you want to have exactly one device doing NAT, and one device (probably the same one) providing addresses via DHCP. I think the second is what Apple calls "distribute addresses"; you need to turn on NAT as well. Then all the machines using the airport will be assigned private addresses like 10.1.0.1 or 192.168.1.1, and the airport will rewrite packets going through it to translate them all to the external address.
posted by hattifattener at 9:49 PM on November 21, 2007

What you want to do is set up the Airport as a DHCP server and use NAT to let all your Macs talk to the Internet over the one fixed IP. The options you want to look at are "Distribute IP addresses" and Share a single IP address (using DHCP and NAT)".

You'll need to set up a DHCP range. The defaults should be fine but if you feel the need to change them make sure you use networks in the reserved private network space (10.x.x.x, 172.23-32.x.x, 192.168.x.x). I think there's a place in the Airport utility to set a DNS server, and if you can find it, set the DNS server IP you got from your ISP on the Airport.

Once DHCP and NAT are set up, set your client Macs to use DHCP to get their IP addresses. If you were able to set up the DNS server on the Airport turning DHCP on for the clients should be all you need to do, otherwise you'll need to set DNS servers for each client.

And unless you want to offer free Internet to anyone withing range You'll probably also want set up some security for your Airport. I use NIC based access lists and 128-bit WEP, but any of the password-based options should be good enough.

If you get stuck, try looking at the help for the Airport utility. It's pretty good.
posted by mexican at 9:56 PM on November 21, 2007

How do I turn on NAT? I already have distribute addresses set up, and it mentions that NAT and DHCP will be used to share a single IP address.
posted by 235w103 at 10:02 PM on November 21, 2007

Argh. Okay. So far-
The Airport is set up like so- Manual IP address, distributing IP addresses, sharing a single IP address, with the DNS already in. This is how I had it set up before. But it's still only letting me connect by Manual IP, with one computer.
posted by 235w103 at 10:12 PM on November 21, 2007

Well, that sounds like the right settings to me.

If you set the computer to "Configure IPv4: Using DHCP", does it receive an address? (It's in the Network pref pane, select the networ interface you're using and click "Configre...". Might take a few seconds.)
posted by hattifattener at 10:22 PM on November 21, 2007

Yeah, it does. It comes up with the IP address of the Airport, plus one. But it still doesn't pull up any pages.
posted by 235w103 at 10:31 PM on November 21, 2007

Get a real router for less than $25 and avoid the whole Airport silliness altogether, this Thanksgiving and into the future.
posted by gum at 11:18 PM on November 21, 2007

Are the computers set to get their address via dhcp (as opposed to static leases)?
posted by philomathoholic at 11:28 PM on November 21, 2007

Oh, right. never mind me.
posted by philomathoholic at 11:29 PM on November 21, 2007

make sure the dhcp is set up to send the client the "router" option, which sets the default gateway, which through a series of features gives the laptop internet access.
posted by rhizome at 11:31 PM on November 21, 2007

"... sharing a single IP address, with the DNS already in ..."

Don't quite get what you mean by that.

Anyway, you haven't got anything in the Access Control tab, have you? If you have, it'll only allow access from the PC with that MAC address.

"It comes up with the IP address of the Airport, plus one. But it still doesn't pull up any pages."

Sounds like DHCP is working (presumably from the router, since you've got "Distribute IP addresses" turned off in the Airport). What does the Airport have set as the DNS server? If it's got the router address, make sure you've got DNS relaying turned on in the router (or put your ISP's DNS server in the Airport manually).

Can that computer ping an IP address?
posted by Pinback at 11:31 PM on November 21, 2007

(Frankly, the easiest way of setting up the Airport is to set "Configure:" to "Use DHCP" so it gets all the details from the DSL/cable router, and "Distribute IP addresses" to "on", assigning a pool of RFC-whats'is'name addresses different to that of the router i.e. 192.168.1.x <=> 10.x.x.x.

This'll work for everything except iTunes sharing between wired and wireless networks.)
posted by Pinback at 11:39 PM on November 21, 2007

It works!
I was just sitting here, pondering, and I wondered what would happen if I turned Distributing IP addresses off, and then on again.
Which I should have thought of before.
Thanks, everyone!
posted by 235w103 at 8:08 AM on November 22, 2007