Like many small businesses we have taken advantage of the 'free' DSL services offered as part of an existing mobile phone contract. In this case we use Orange for mobile service (we're based in the UK) and they offer 2 Mbit internet with a wireless router for no extra if you have at least one pay monthly account. I thought that it would be a useful addition to our network for testing and backup, especially as it is from a different ISP and delivered over a physically separate landline from our business internet.
The wireless router arrived yesterday and the DSL activation happened on time so that the line came up first time when I plugged the line into the router. I'd heard a few horror stories about Orange's support for Macs so I was pleasantly surprised when I popped the install CD into my MacBook and it came with full OSX installation instructions. 5 minutes later I was surfing on the internet via my shiny new Orange broadband.
Now that we had two internet accesses functioning, how to use them both?
I originally thought that I would keep our 8 Mbit business broadband link and the new line on separate networks so that I would not have to change any server or client configurations, just point my test machines at the new default gateway.
However, with a little thinking about how much work it would be to switch all clients over in the event of a line failure (it does happen), especially if no IT savvy people were available at the time of failure, I started Googling for suggestions on how to link all computers to both gateway routers.
I investigated using a spare Linksys router with new firmware to act as a load balancer, but that would introduce a new single point of failure. After thinking a bit more about OSX's multihoming feature I decided to do the following:
Mac OS X Hints
http://hints.macworld.com/article.php?story=2007101109301541