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So, I bet this scenario is familiar for many people out there.

I've got a 3G "modem" and a ISP connection, in many different places I go, including mac and windows environments.

I want to plug in my 3G and leave it connected along with the ISP. So I'd effectively have 2 different internet connections on the same machine.

While both windows and mac says they are connected, I think they both route the whole traffic to just 1, at random, or using metrics, or whatever. But it's just 1.

There are two problems there: I actually want to use both to maybe get better speeds, and definitely should be able to get a more stable connection - at very least in the sense that one would cover the other if either fails.

That's my current and main issue - I am able to switch internet if one fails, usually from ISP to my 3G. But I have to do it so in a slow and manual process (assigning a manual IP and removing the gateway) if I want to keep the local network connected. Or just manually disable the ISP, in which case it's easier, but I lose the LAN. And then I have to change it back. Plus that times out every dedicated connection I may have - which no BATCH file could solve.

Anyone knows of a good solution for this? I bet there are softwares to do it - what about using just the OS?

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It would be easy enough to script a solution that acts as a fail-over, and as for load balancing, this is the best I could find for just using the OS (windows), I just have no way of testing it: Configure Registry for Load Balancing. For OS X, there is an option that I found that is 3rd party: Crossroads

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"easy enough"? I'm having a hard time just compiling that crossroads, that seem to be exactly what I needed... except for the fact it's hard to use! :P - sorry, I'm just a regular dumb user when I want some useful tool. – cregox Nov 2 '10 at 23:37

The Multi-homed Overlay Network (MONET) research project at MIT aimed to do precisely this.

MONET arose from the observation that access links are often the weakest link in Internet availability, particularly for home users, or users in areas without well-established Internet infrastructures. The traditional mechanism for taking advantage of multiple access links — multihoming with the Border Gateway Protocol (BGP) — is not available to many of these people who need redundancy the most. Our implementation of MONET is a Web proxy that uses an application layer approach to harness redundant access links and multiple paths through the Internet to dynamically avoid network failures.

There is a source tar-ball available but I'm not sure how easy it would be to build and deploy; it's almost certainly Linux/BSD focused and probably hasn't been used actively in some time. It was developed as part of Prof. David Andersen's PhD thesis 5 years ago. He may be responsive to inquiries about it though.

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that sounds very interesting! gonna check on it later. – cregox Sep 22 '10 at 17:54
looks like it's "in beta" and "comming soon" for too long... plus it's no use in my case if it's linux only. :( – cregox Sep 23 '10 at 12:35

I don't know of a way to load-balance or auto-failover on OS X, but I can at least make a suggestion for simplifying the manual failover process: build another network "location" with the service priority order reversed:

  1. open System Preferences, select the Network pane
  2. select Edit Locations from the Location: pop-up menu
  3. select your current location, and select Duplicate Location from the action menu (gear icon) under the location list)
  4. edit the new location name to something descriptive
  5. click Done to dismiss the edit location dialog
  6. select the new location from the Location pop-up, and click Apply at the bottom right
  7. select Set Service Order from the action (gear) menu under the "service" (network port) list on the left
  8. drag the services around to swap the order of the 3G and ISP (ethernet/airport/whatever) connections; the one listed first will be preferred for internet access
  9. click OK to dismiss the service order dialog, then Apply again
  10. pull down the Apple menu; you should now have a Location submenu that'll let you quickly switch between the two locations
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yeah, I've toyed with locations already. they also work to fix temporary issues with the network, rather than rebooting I just change location some times. – cregox Sep 22 '10 at 17:55

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