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How They Shut Down The Web
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An expert analysis of Internet traffic:
There's no question that something large happened in the Iranian telecom space, and that the timing aligns with the close of voting and the emerging controversy...
What can we say for sure? Not much, except that Iran remains well-connected to the Internet from a routing perspective. If I had to guess, I'd say that there are probably a lot more people around the world pulling local content from Iran's providers right now, and that surge of demand is probably contributing to increased congestion and (perhaps) some of the route instability we see. It wouldn't be unusual for there to be some inbound cyber-mischief as well, from supporters of one or the other side, but so far we only have rumors on that front.
There are six of them: Turk Telecom (TTNet, AS9121), FLAG (AS15412), Singapore Telecom (AS7473), PCCW (AS3491), Telia (AS1299), and Telecom Italia Sparkle (AS6762). As the following plot shows, five of them lost Iran's transit, and one of them (Turkish Telecom) was a big gainer. (Red arrows indicate loss of transit preference from the outside world; green indicates a gain in transit via the given provider.)
A transit shift of this magnitude may indicate that something (administrative, or physical) has affected Iran's connection to the submarine cables running east and west not a total outage, but some kind of significant impairment. Turkey has their own, interesting arrangements with Iran for transit, and those are still in good shape (perhaps somewhat congested, having presumably doubled or tripled in transit volume).
It wasn't unusual to see 300ms traceroutes from North America and Europe in this timeframe to many Iranian sites. Of course, you have to remember that globally visible routes are the signposts for inbound traffic to and through DCI to the local providers; from the outside, there's no telling what the Internet experience of the average person inside Iran is like today. It sounds as if a lot of content is being blocked within the country. It is interesting to note that the changes in routing that took place were very specific in their impact on DCI's various transit providers, who keep the country connected to the world.
