You can’t get there from here

March 17, 2008 Earl Zmijewski

Cogent and Telia are having a lover’s quarrel and, as a result, the Internet is partitioned. That means customers of Cogent and Telia cannot necessarily reach one another. This was not due to a configuration error or a physical cable break. This is the way the Internet works and sometimes doesn’t work. If the businesses that run the show don’t play nice with one another, their customers can pay the price of being cut off from parts of the ‘net. At least when Pakistan mistakenly hijacked YouTube, the matter was sorted out in hours and did not require the cooperation of Pakistan. The Cogent/Telia tiff has been going on for 4 days now and only they can resolve their differences. The rest of the world can only hope for full connectivity to be restored.

When relationships end, it’s often hard to figure out the one thing people really want to know: who dumped whom? The politically correct thing to say is that the two parties had irreconcilable differences or that they had simply grown in different directions. That all sounds nice, but in fact, it’s typically the case that one party called it quits, leaving the other broken-hearted. Although routing data don’t show who pulled the plug, the word on the street is that Cogent jilted Telia last Thursday, ending their long-term peering relationship. The result is that the Internet is now partitioned. Downstream customers of Telia and Cogent can only reach each other if they also have providers other than these two. If not, they are out of luck as Cogent plays the Internet equivalent of chicken with Telia.

So let’s look at the facts. On 13 March 2008 at 22:03 UTC, we saw the link between Cogent (AS 174) and Telia (AS 1299) disappear. The way this looks in the routing announcements is that all AS paths with “174 1299″ or “1299 174″ on them vanished, meaning there is no longer a physical link between these two providers. At this point, Telia lost direct access to 4474 prefixes (networks) transited via Cogent, whereas, Cogent lost 1633 Telia networks. Now, you might be thinking, “So what? Won’t the Internet just route around the problem, finding alternate paths?” Well, yes if there are alternate paths to be found and if the players actually allow traffic to flow via them. For around 12 hours, most Telia customers did access Cogent via Verizon (56% of the 4474 networks), Level 3 (16%), AT&T (6%) and others, but then that abruptly stopped. We’re guessing it’s because Cogent eventually slammed the door shut on these alternate paths to their network from Telia, since none of Cogent’s customers accessed Telia via alternate routes during this time. Like divorce court, depeering is supposed to be painful, otherwise you might not get what you want. You only hurt the ones you love.

So now we have a bit of a problem. Customers who ultimately rely solely on Cogent for transit cannot get to Telia, likewise for customers downstream of Telia. So where are these customers exactly? The following tables show the geo-location of those networks downstream of Cogent that cannot reach Telia and vice versa for Telia.

Telia cannot reach Cogent
Country # Prefixes
US 1868
Canada 232
France 98
Spain 41
Germany 31
UK 27
Others 86
Cogent cannot reach Telia
Country # Prefixes
Sweden 444
Finland 322
Russia 153
Poland 113
US 73
Latvia 62
Bulgaria 52
Spain 40
Denmark 35
Norway 30
Others 249

Given the markets Cogent and Telia operate in, these lists are not too surprising. What is surprising is that networks in the US are actually cut off from each another, since a largely US provider is playing hardball with a largely European one. For the Internet to be whole again, Cogent and Telia need to kiss and make up. No one can force either one to carry traffic destined for the other. But my guess is that Telia is hearing more grief from Scandinavian customers not being able to reach US content than Cogent is hearing from US customers cut off from Northern Europe.

Of course, the list of impacted networks is too long to be included here, but they include a wide range of commercial, educational and government clients. On the Telia side, the victims include the Swedish Defense Data Agency, the Finnish State Computer Center, and broadband customers in St. Petersburg. With regard to Cogent, Blue Cross and Blue Shield of Delaware, Kansas State University and Reuters America were all collateral damage.

But people can and do de-peer all the time for business reasons without blowing holes in the Internet along the way.Early on 14 March 2008, Flag (AS 15412) and SingTel (AS 7473) parted ways, but almost all of the few thousand networks carried between the two managed to find alternate paths via their peers or providers. That’s because neither tried to “stick it” to the other and allowed Internet routing to do what it does best, find another way to get from here to there.

The post You can’t get there from here appeared first on Dyn Research.


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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