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What actually makes this work?
Authored by: diroussel on Aug 26, '04 04:29:59PM

Any one got any ideas how to do with with other routers? I've got a Linksys WRT54G, and I'm I would like to replicate this neat trick.

As far I was aware DHCP allocates IP address per MAC address on a lease basis, and since the AipPort and Eth adaptor have a different MAC they get given different IP addresses? What is it in this hint that allows it to work?

Surely when you disconnect the LAN cable there is no time to release the lease on IP, so how is that IP still free to be reallocated to the AirPort.

I have a linux server I could use as a DHCP server, and I believe my router has bridging capabilies (although I've not tried them). Any one got any ideas for me to try?

Thanks, Dave

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What actually makes this work?
Authored by: Brock Lee on Aug 26, '04 06:20:59PM

The key to the initial post is this phrase "configured my own DHCP server". Most DHCP servers (e.g., that you'd run on a server running Linux or BSD and not on a wireless router) allow for the setting of mappings from specific MAC addresses to specific IP addresses. The WRT54G does not offer this capability.

I understand there is some 3rd party firmware out there that adds extra capabilities to the WRT54G. Whether this level of control is one of the capabilities, I do not know.



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What actually makes this work?
Authored by: pecosbill on Aug 26, '04 07:02:27PM

Since it's YOUR LAN, why not just set up a network location for your LAN and assign a static IP address to each interface that's the same (not using DCHP at all)? Sounds like it would do the same thing but without the DHCP challenge.

---
Pecos Bill



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What actually makes this work?
Authored by: crispyking on Aug 26, '04 07:20:22PM

Right, I'm running my own DHCP server on my LAN, but if you're not running a DHCP server, you should be able to set the IP address manually in the Network System Preferences.

There are two tricks that make this work. The first isn't much of a trick: you just configure the wireless AP to be a simple LAN bridge. It simply bridges ethernet traffic between the LAN and the wireless network, so it basically operates transparently like a hub or switch. I would think you could do this with any wireless AP.

The second trick is to configure the wireless interface to have the same IP address as the wired one. This is the real trick since you're really not supposed to configure more than one interface on a given subnet. It's a bit of a hack since all the other machines on the LAN see the MAC address changing for that IP address and complain in the log file in case it's a spoofing attempt. But they change their ARP caches anyways and everything continues to work. It's the fact that Mac OS X allows you to set the same IP address for multiple interfaces that makes this work.



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It's not as complicated as you think...
Authored by: jtrott on Aug 27, '04 04:17:27AM

I don't think you actually need to do any configuration on the DHCP server at all. I've been using the same setup (moving from lan to wireless without dropping connections) for a while now. The secret is to set your DHCP Client ID to the same on both interfaces. As an aside, if you set it to the same as in your Sharing control panel and make it a single word with just letters and numbers (no spaces), the DHCP server will record your client name and correctly configure dyndns (if you have it setup).
In short, make your DHCP Client ID the same on both interfaces and make the Sharing Computer Name the same again to make sure that the DHCP client name is recorded correctly on the DHCP server. There is no need to mess with the DHCP server configuration.
HTH,
JT



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It's not as complicated as you think...
Authored by: crispyking on Aug 27, '04 12:08:21PM

It depends on the situation. I tend to prefer making changes on my DHCP server so I don't have to mess around with each client machine's settings :-)



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It's not as complicated as you think...
Authored by: jtrott on Aug 30, '04 07:40:24AM

Well, I prefer to change my iBook setup, rather than all the DHCP servers I come in contact with in a normal work day :)
To each their own I guess ;)
JT



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