Redundant Connections to a Single Host?

Part 1: Internet Redundancy, Or Not

Previously I wrote about how true redundancy for Internet connections is only available to Internet providers and very large enterprises. This post continues from there.

I would guess that the fact that it’s not possible to get redundant Internet access is a big surprise to people who haven’t look into it in detail. Surprisingly though, if you have a smart phone or a laptop that you plugin to an Ethernet port, you live through the problems caused by this Internet protocol design flaw every day. These problems seem so normal that you may have never considered that reality could be otherwise.

Let’s start with the example of a laptop attached to a docking station at your desk. It’s very common to use the wired Internet connection at your desk vs. wireless because it typically offers faster, more consistent service. Consider the case of needing to transfer a large file while working at your desk. You start the transfer, it’s humming along in the background, and you switch over to another task. A few minutes later you remember that you have a meeting so you yank the laptop from its docking station and walk to the meeting room.

What just happened to the file transfer? The answer of course is that the file transfer died and you may be thinking, “Of course it died. The laptop lost its connection”. This seems normal because we’re all used to this brokenness.

Think back to the previous blog post. We were trying to get redundant Internet links to a small business and households and found that it’s not possible with the Internet protocols as they exist today. Now think about what the laptop is – it’s a computing system with two Internet connections. This really isn’t very different from a network with two connections. Ultimately, the reason the file transfer died is because of all the same limitations discussed in the last post related to network redundancy. That is, solving the problem of enabling multiple redundant connections for a network, solves the problem for individual hosts as well.

Now consider a smart phone user that starts a Skype voice or video conversation while in the office and then heads to the car to go meet a client. If you’ve accidentally tried this before you know that as you leave the range of the office Wi-Fi, the connection drops. In the particular case of Skype, it may be able to rejoin the conversation after the phone switches to the cellular data connection but most applications don’t even make an attempt at this. Like the laptop, a smart phone is just a computing device with multiple Internet connections.

One last example, your office server that runs Active Directory or performs some other important function. You probably would like network redundancy for this as well right? This also isn’t possible without low level ‘hacks’ like bonding two Ethernet ports to the same switch together.

Not only does the Internet not allow for true redundancy for networks, the lack of this functionality causes trouble for end hosts as well.

Part 3: Detecting Failure

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