15th Century Routing

September 25, 2014 Earl Zmijewski
Which way is up?

Since I sometimes find myself hopelessly lost, I tend to wonder about global navigation in the days before GPSes or even accurate maps. I imagine you started off with just a general idea of where you wanted to go (e.g., “The New World”), crude navigational aids (the stars, Sun and Moon when you could see them), and hearsay from your fellow travelers or the locals about your proposed course. In addition, you only had a view of the world from your current location, limited by the curvature of the earth.

Looking for trouble

Thinking about it, this sounds a lot like modern day routing. You have a general idea of where you want some packets to go (a network prefix) and very crude navigational tools (BGP updates), most of which are hearsay from peers, providers and random strangers you have no reason to trust. Plus your world view (routing table) is limited to the place where you collect your routes and from whom you collect them. There is no comprehensive map of the world (global routing table) or any reason to believe that your packets won’t fall off the end of the earth (be blackholed) when you send them on their way. The lack of a global routing table is the reason Renesys has to collect routes from all over the world (over 250 places at present) and the reason we see around 330,000 routes, compared to what is currently considered a “full table” at just under 240,000 routes. Compared to modern navigation in the physical world, it seems like we would have a better way to route Internet traffic by now.

Single homed

Conveniently, Renesys is located in New Hampshire where real life navigation can remind you more of the ancient world than the modern one. (Maybe that’s why we’re good at Internet routing?) Our physical maps are often wrong, showing roads that no longer exist or landmarks in the wrong locations. Cell service comes and goes and doesn’t even work at my house, in a neighborhood less than 2km from Dartmouth College. And it is often so cold that battery life is limited to minutes; so even if your GPS did work, it would be dead when you pulled it from your pack.

Happy not to have been blackholed

With this in mind, we ventured out on a Renesys team-building exercise on Sunday, 20 January 2008. We picked this day to go above tree line since the weather forecast was particularly nasty. A storm was coming and the highs for the day were supposed to drop to -26C on the peaks with wind speeds exceeding 100kph. Luckily, we got to the top ahead of the storm and the day was absolutely brilliant and comfortable: -22C with a cooling breeze of 50kph. Our routes were clearly visible and no one was blackholed – a very successful day of navigating the mountain.

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About the Author

Earl leads a peerless team of data scientists who are committed to analyzing Dyn’s vast Internet Performance data resources and applying their expertise to continually improve upon Dyn’s products and services.

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