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I've recently been assigned a static IP by my ISP provider (Sonic.net). My previous setting was with the modem configured to connect using static IP and the Airport Extreme as a bridge. NAT and DHCP were done at the modem, but I couldn't get WOL (Wake On LAN) to work (an Apple technote specifies that this setup won't).

Now I've set up my modem as a bridge and configured the Airport Extreme to handle everything. I've set it up as a static IP and activated DHCP and NAT. I can connect to the Internet perfectly and everything else (connection-wise) works. Yet to try remote access and WOL.

The only problem is that I can't access the modem's admin panel. This should be at 192.168.1.1, but I can't get to it. I think the Airport Extreme is assuming .1 as its internal address.

Is there any way to access the modem in that setup unless directly linked to it (by Ethernet cable)? Will giving the modem another IP (say .201, out of Airport's DHCP range) work? Can I change the Airport's internal address somehow?

EDIT: I've managed to assign the modem an IP of 192.168.0.1, so it should be in another subnet, but this traceroute shows it hopping out after hitting local router.

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The problem isn't just that you have two devices using the same 192.168.1.1 IP address, but also that two network segments are using the same subnet (the first 3 parts of the IP, 192.168.1.x). If you're on the AirPort's LAN at 192.168.1.123 and you try to talk to the modem at 192.168.1.1, the network sees "192.168.1" and recognizes it as local traffic, meaning that it never goes out the WAN port where the modem is.

It's sort of like if I try to mail a letter to "123 Fake St, London". I mean the one in England, but there's a city called London right here in Ontario, so that's where the post office is going to send it.

Anyway, when you made your own subnetwork with NAT, you should have picked a new IP subnet to go with it. The AirPort utility calls this part of the IPv4 DHCP range, even though it affects more than DHCP. It's probably currently set to "192.168.1.100 to 200". Just change the third part to something else, like "192.168.0.100 to 200". This will move your entire LAN to the 192.168.0.x subnet, and the AirPort will take 192.168.0.1 for itself.

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  • I connected to the modem via Ethernet cable and managed to access the admin panel. I changed its IP to 192.168.0.1, so now they should be in different subnets, but I still can't reach it while connected to the Airport Extreme.
    – Reven
    Nov 2, 2012 at 12:58
  • Can you run traceroute 192.168.0.1 in Terminal and paste the result into your question or pastebin? It might give some useful information. I have a similar setup and I think I've had trouble connecting to my modem at times, but right now it works normally.
    – gabedwrds
    Nov 2, 2012 at 13:13
  • I've added a pastebin and edited the post.
    – Reven
    Nov 2, 2012 at 21:51
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    My best guess is that the modem is simply ignoring you. Because of NAT, your router is identifying the outgoing traffic as coming from 75.x.y.2, and the modem might intentionally only allow access from within 192.168.0.x.
    – gabedwrds
    Nov 2, 2012 at 22:14
  • That's a good point. I hadn't thought of that. I'll try to hook up directly to the modem again and make access to the admin panel more permissive.
    – Reven
    Nov 2, 2012 at 22:33
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The way to do it would be to edit the firewall on the router. Assuming your modem's address is 192.168.0.1 (and your router side network is on 192.168.1.x), using the DD_WRT firmware it would be as easy as adding:

ifconfig `nvram get wan_ifname`:0 192.168.0.2 netmask 255.255.255.0

to the init scripts and the following to the firewall:

iptables -t nat -I POSTROUTING -o `nvram get wan_ifname` -j MASQUERADE

Unfortunately, there is no way (that I know of) to accomplish this with the Airport Extreme; from what I've been able to gather online, this can't be done.

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