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Sharing a printer via Rendezvous across sub nets Network
I wanted to share my USB printer with my roommate's Mac. It wouldn't work - no printer would show up in the Rendezvous pane of the Add Printer dialog. It turns out the problem is with AT&T Cable; or rather, the way it does things.

AT&T Cable in San Francisco is an odd beast. Their central will hand out DHCP addresses to any host connecting to a cable modem - rather nice, since you get a mostly-static global IP address for each machine (at least four allowed per household), nor is a "router" required - a hub is plenty enough. Sadly, the IPs they hand out are rarely on the same class C (Subnet Mask 255.255.255.0) network - the network mask their DHCP server hands out! What this means is that Rendezvous will not work between machines in the same house.

The solution is to give the machines a secondary IP address which is on a shared IP subnet. My method is to use the command /sbin/ifconfig en0 alias 192.168.1.?, where ? is a number between 2 and 254 - different for each machine. The 192.168.?.? subnet is "private," which means it won't colide with any global addresses.

This solved the problem instantly. A little bit more work, and I had a startupItems script put together as well (contact me for details) that adds the alias every time the machine boots.

It is VERY cool to be able to share a USB printer between two Macs with nearly no effort.
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Couldn't you just...
Authored by: dave@mmu on Jan 30, '03 10:55:43AM

Hi, rather than using that method, i think you could just create a duplicate of your network connection in System Prefs:Network:Show:Network Port Configurations by selecting your "Build-in Ethernet" (or whatever you use) and clicking the "Duplicate" button. This will then allow you to create a whole new set of IP details running off the same port as the original one. Easier than making a startup file anyway.
Dave



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Yep, you can just...
Authored by: smeger on Feb 03, '03 01:58:12AM

This worked for me. I have a complicated setup with a desktop mac that has a static IP. It provides a dynamic IP for an airport basestation, which provides dynamic IPs for two wireless iBooks. I wanted to be able to print to a USB printer connected to the desktop machine.

I duplicated my built-in Ethernet entry in Sys Prefs -> Networking, gave the duplicated item (Built In LAN) a static IP in the same subnet as the ones provided by the Airport base station, and set the order of the network ports so that the static, outside-world IP was first, and then the internal subnet IP. Worked like a charm!

Thanks!



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Couldn't you just...
Authored by: tenenb on Feb 03, '03 09:15:15PM

This seems right, but could you explain a bit more ?
I tried this, giving non-routable adresses to 2 macs, eg 192.168.0.x and 192.168.0.y, but then the conection was not shared any more, and I still couldn't print from one mac on the other's printer.
So, to summarize, how can you share a DSL conection on a local network and also share a USB printer?
many thanks in advance if you cna help.



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Airport and Ethernet network
Authored by: matthewd on Feb 02, '03 12:32:12AM

I'm in a similar situation... helping to set up a friends home/office with Macs and one pc. There are two iBooks on an Airport network (Airport (snow) base station is connected to the hub) and two G4's running on a broadband connection via the ethernet hub.. The two G4's get an ip address in the range of 192.xxx, whereas the two iBooks use a 10.xxx range.. would your suggestion also work here so that all computers could share a usb printer shared on one of the G4's ?..or is there an easier way !.. thanks!



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Airport and Ethernet network
Authored by: Bottacco on Feb 05, '03 08:09:33AM

Airport Base Stations usually come preconfigured to work under 10.x.x.x private address space, but you can change that editing the Base Station (ABS from now on) configuration with the AirPort Admin Utility. There are two easy solutions for your particular problem:

- OPTION A:
change your G4s' IPs to match the AirPort Network's IPs so all of them are in the 10.x.x.x so no routing is needed between them... but you will have to change the internal IP assigned to your ADSL o Cable router (you don't say what type of connection you have) because it sure has one in the 192.168.x.x range, like your G4s. You may have trouble if DHCP is enabled for the hole 10.x.x.x range, but can change that with the AirPort Admin Utility.

- OPTION B (preferred by me):
or you can edit your ABS Station configuration and so it works in the 192.168.x.x range. You don't say if your ABS is serving IPs to the iBooks or they are configured with static IPs. If you need the ABS to serve IPs under the 192.168.x.x range configure it just to handle part of that range (like ten IPs only) so they don't have conflicts with the IPs assigned to other machines or the router.

I hope this helps.



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Re:Airport and Ethernet network
Authored by: matthewd on Feb 07, '03 05:12:25AM

Hey thanks Yeti.. that looks promising.. You'll have to give me a few days before i can contact my client and try this solution.. will let you know.. thanks again.



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Great hint! But why doesn't this happen automatically?
Authored by: derrickbass on Feb 05, '03 05:40:27AM

Finally, I can share my printer!

Now, the question for any Rendezvous experts out there... Isn't this exactly what Rendezvous is supposed to do automatically? Shouldn't all the computers connected locally assign themselves addresses in the ZeroConf range? I've discovered experimentally that this does happen if I disconnect my cable modem, but if the computers are connected to the internet, Rendezvous seems to use their assigned IP addresses rather than creating Rendezvous addresses. Does anyone know why that is?



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A little bit of theory
Authored by: Bottacco on Feb 05, '03 11:41:54AM

Private address space (192.168.x.x , 10.x.x.x and 172.16.x.x) is termed as non routable- non Internet enabled and is defined by RFC 1918. That RFC prohibits addresses in those blocks from being seen in the Internet, either as source or destination addresses. That RFC also requires that addresses in those blocks be filtered at the edges of networks. Some providers and enterprises do this filtering, some don't, but in any case, routes for those destinations will never be found in the Internet.

If you are using one of those addresses as the local address on your computer, unless you are doing NAT or something similar to translate that address into something that is allowed on the Internet, the network will not know how to send traffic back to you. These addresses were intended only for local use within your network, not outside of it.



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