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I'm running a Windows 2003 single domain network. We currently have a single connection line run in to an inbound nic in our ISA firewall. Outbound nic goes to a switch and from there to all other workstations / servers. I'm interested in adding another line so that outbound web services can utilize one line which all other traffic could utilize the second. In the event of an outage I'd be interested in having all traffic bumped over to the still active line. Is this possible? Would I have to split our network into two distinct domains? We run an internal DNS, would this greatly complicate things? What basic steps are involved?



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Related question .. has at least one solution that will do what you want .. – tomjedrz Aug 25 '09 at 17:39
up vote 2 down vote accepted

I think you're asking about what it would take for you to utilize multiple connections to the Internet for fail-over.

Fortunately, your Active Directory domain and internal DNS has little to do with such a scenario. Microsoft ISA Server doesn't natively support using multiple WAN interfaces simultaneously.

One solution would be to deploy a "multi-WAN" or "dual WAN" router in front of the ISA server. These are devices that perform rudimentary load-balancing and failover using multiple Internet connections. There are a variety of price-points and feature sets, so you'd do well to shop around and compare reviews.

You'll never get the full bandwidth of both Internet connections to be "shared" for a single TCP connection (a single download, etc) w/o cooperation from the ISP on the other end. W/ consumer / prosumer "multi-WAN" routers the best you can hope for is that the router would try and intelligently send new outgoing TCP requests over the less-congested link.

BTW: I've seen a couple reviews of these Peplink Balance routers just doing a rudimentary search. They're not inexpensive, but they appear to be fairly solid.

If you want to take a different approach you could cobble together some rudimentary failover using a script (like the one in this discussion) to test the availabiliy of a connection periodically and, if necessary, swap the default gateway to another connection. I suppose it would work, but I'd rather have such functionality happening in hardware.

There was a product called "RainConnect" that had both inbound and outbound failover and load balancing capability on ISA Server, but the product has been discontinued, to my knowledge (when the manufacturer was acquired by EMC).

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A multi-wan router is an excellent suggestion. There is definitely more to the solution than that specifically but it is a great addition. Thanks for the comment. – JohnyD Aug 31 '09 at 15:26

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