Sharing my internet connection TO an airport extreme? How can I do this..

Question

Hi,
My Mac Pro is connected directly to my modem on Ethernet port 1 (Eth-1).
The connection is solid and my Mac Pro can browse the internet.
What I am now trying to accomplish is to share my internet connection with my family who is using an Airport Extreme Base Station.
My setup is as follows:
Modem --> Mac Pro on Ethernet 01.
Inet Sharing on Mac Pro via build-in airport card == Wifi, works.
Inet Sharing on Mac Pro via Ethernet 02 --> AEBS WAN Port == Wifi & cabled connections do not work.
How can I get my AEBS to accept this shared connection, using this shared connection as the source for the internet that is being shared from the AEBS to both, Wifi and Cable, connected clients?
The reason for this setup is that normally my family has their own modem & isp which connects to the AEBS but the modem has broken and it will be a week until the replacement arrives so I need to share my connection with them until then.
The distance between my shared wifi and their AEBS is too far, which is why only having the working wifi is not good enough.
Any help would be much appreciated as I have spend the last 2 hours trying all kinds of configurations to no avail.
Thanks for reading,
Jannis

Answer 1

Hi,
I currenly have a DSL modem that is a router as well and is WiFi able.
This gives me one LAN with no subnets as there is no other routing device.
Previously I had DSL modem that did DHCP (Issued IPs) but did not do WiFi so I had a Wifi Router, which also did DHCP by default. This is two overlapping subnets (modem > Router > Computers(s) AND Router > Computer)
Because the WiFi router is effectively fairly dumb it passes on any routing info from the modem.
This means the computer(s) get two IPs although System Preferences > Network can only show one.
What I did was set the DSL Modem to not do DHCP.
The Router then needs the IP of the Modem (Gateway), the DNS servers, the Subnet Mask entered in the boxes that usually appear for Static Routing. You also need to tell the Router to use on IP that is in the range the Modem is using.
This stops the overlapping subnets and makes the LAN more Linear.
Modem > router followed by Router to Computers(s)
Now your Mac Pro is taking the place of a Router and arguably a WiFi Base Station.
Re 1)
If Internet Sharing is set to do Ethernet (from Modem to Mac Pro) to Wifi I can't see that it can be set to do Ethernet (1 as you call it) to Ethernet (2) to get to the Airport Base Station.
I take it the Airport Base Station cannot "See" the Mac Pro's Wifi ?
Ideally it should be set to Bridge (Off) Mode - Not doing DHCP) so that it extends the range of the Mac Pro's WiFi network.
Re 2)
If the Base Station was in Bridge Mode then all the other house's computers would get IPs from the Mac Pro's subnet.
If it is Sharing an IP then they get their own Subnet from the Base Station.
Depending on what range the Mac Pro Uses and the Base Station is set to, you may get conflicting IP addresses.
To a certain extent Subnets can be useful as long as they are separated properly and Linear.
Consider it this way.
The Postal Service uses House numbers and street names in overlapping subnets to deliver mail.
The White House (as computer) is in Washington (router) which is in the USA
Now think of a house on a corner plot. Before city planners or postal service gets their hands on it it possibly could be considered to be house 30 Main Street as well as house 1 Side Avenue. Technically a letter could be addressed to either 1, Side Ave or 30, Main Street, Imaginary Little Town.
On the other hand the upstairs of you house is part of that house (in the same LAN) However it can only be accessed by the stairs (Separate, linear Subnet).
Certain apps can deal with/ignore overlapping subnets but others need the set up to be more linear. (iChat and other IM apps are one sort)
I hope this helps some more.
8:20 PM Monday; April 19, 2010