what you want to do is setup your express to be a "bridge" for your airport extreme network, you want to create a "new" wireless network (but if you use the same settings as your extreme, most macs should seamlessly work and switch as required)
make sure your airport express is configured not to do any NAT or give out IP's as that is maybe what is conflicting with your network currently, also make sure you give it an IP in the same subnet as your airport extreme and also that it does not conflict with any other machines
Consider the following tutorial
mactip.net
Admittedly it only covers ethernet to wireless or wireless to ethernet, however the same steps should apply for this setup (wireless to wireless).
Make sure of the following:
- The incoming wireless has a dhcp lease auto assigned
- The outgoing wireless on the laptop has a manually assigned ip, the subnet matches the incoming wireless, and that the router field is populated with your dhcp server (router)'s ip.
Here is my configuration (I am using an ethernet to wireless bridge but the principle is the same)
Example incoming wireless
Example outgoing wireless
Lastly verify that your old laptop has the correct version of the bootpd service running.
sudo launchctl list|grep bootp
26987 - 0x7fc881d5b9e0.anonymous.bootpd
Important!
While you will be able to get internet access to any device connected wirelessly to the old laptop, those devices will not be able to communicate with any other devices on the other side of the old laptop.
This is because the old laptop is running a dhcp server and the devices will be in a different subnet.
To prove this, take a look at ifconfig on the old laptop. You should see a new network device called bridge0.
bridge0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether ac:de:48:e4:39:77
inet 192.168.2.1 netmask 0xffffff00 broadcast 192.168.2.255
Configuration:
priority 0 hellotime 0 fwddelay 0 maxage 0
ipfilter disabled flags 0x2
member: en1 flags=3<LEARNING,DISCOVER>
port 5 priority 0 path cost 0
On my network, all devices that connect to the internet from my 'old laptop' get a dhcp address starting at 192.168.2.x. Those devices can not connect to any device in the 10.4.90.x subnet.
You may be better off buying a wireless repeater, or purchasing a directional antenna for your usb wireless network card.
Best Answer
You can suspend a command in the bash shell using control-Z. To resume the command, run
fg.