Telstra Cable

If you live in the Wellington area then you might have cable from Telstra. The modem is a single port modem that does not act as a router. Setting this is somewhat trivial as it is merely a matter of adding the IP Address to the Internet Settings under Airport Utility like so:

• You need to set Configure IPv4 to Manually as the modem doesn't have a DNS server.
• The IP Address is the address given to you by Telstra and will be something like 172.51.1.60.
• Subnet Mask is generally 255.255.255.0 and in fact it is that under Telstra.
• Router Address is generally called Gateway on most networks and I'm not sure why Apple chose to call it Router Address as it can be confusing. That being said it should be the same as your IP Address only the last number will be a 1 instead of for example 60 so it should look something like this: 172.51.1.1.
• The DNS Server(s) field needs to be filled in for Telstra but I forget what these are. These should be on the document Telstra left when the service guy came to install your modem.
• The Domain Name isn't really used and it's best just to leave this blank. You can add clear.net.nz‚or paradise.net.nz if you wish but it doesn't really make much difference.
• To share this connection however ensure that the drop down box labelled Connection Sharing is set to Share a public IP address which should allow you to see the tab labelled DHCP.

• This box for the most part can be left as it is. By default DHCP Beginning Address is set to 10.0.1.2, but the other options are 172.16.1.2‚and 192.168.1.2...but 10.0.1.2 is fine for now.
• DHCP Ending Address can be left alone as well and will automatically change depending on which IP Address range you selected. 200 is at the max end of the IP Address range with 255 being the absolute maximum but it is not recommended to go that high. You can lower this range if you wish but if you have say 5 machines it pays to go no lower than 7 just to allow a bit of leeway in case you get stuck IP Addresses.
• Now click Update and your Airport Extreme/Express will reboot with the new settings.

ADSL Modems‚

Even a single port modem has a built in DHCP server and this plays havoc when trying to share with a router. In the Airport Utility screen select the Internet tab and you should see a screen like so:

• Like the Telstra settings above you need to set the Configure IPv4 to Manually. The difference here is that the settings on this screen (except maybe the Domain Name) should be set pretty much the same here.
• The IP Address should be set to 192.168.1.2 as it is the next in line to the modem itself and as such the router should have an address before all other machines on the network.
• Subnet Mask needs to be 255.255.255.0 and the Router Address needs to be 192.168.1.1 so as to point it to the modem.
• DNS Server needs to be set to 192.168.1.1 on account of the fact that the DNS server is on the modem itself.
• Once again Domain Name doesn't need to be set.
• The big difference between the above Telstra setup and this is that you need to change Connection Sharing to Off (Bridge Mode). This is what threw me. I tried to have the default but Airport Utility kept throwing up an error about Double NAT (Network Address Translation) which is how a machine on a local network can connect to a machine on the Internet. Turning the Airport to Bridge Mode bridges the two networks together. This prevents the Airport from distributing IP Addresses while the modem itself is trying to distribute IP Addresses.
• Click Update.

This is a quick and easy way but if you want to keep all IP distributions with the Airport you should be able to turn the DHCP server off in the modem via the web page and set up the Airport using the above Telstra Cable method.

This tutorial was written on the basis of Telstra modems being Motorola and the ADSL modems being Dynalink as is the case with Orcon, Telstra ADSL and Telecom. Some settings may be different depending on what your modem is.