Analysis: ISPs accused of blocking Netflix — the mystery solved

It seems the mystery has been solved over why many NZ users have been having problems accessing Netflix, the popular, US-based movie and TV show streaming service.

A large mob of NZ Netflix users have been trying to work through technical issues on Geekzone and social media since over the past couple of days.

And there's been no shortage of conspiracy theories.

ISPs have been accused of messing with Netflix traffic, but they've comprehensively denied shaping or throttling.

And the best geek brains tried to work out if upstream providers like Level 3 (the big US telecommunications outfit that sells bandwidth to NZ ISPs, among others), might have advertently  or inadvertently  disrupted internet traffic to this part of the world. But to cut a long story short, that theory didn't hold water.

That left the uber conspiracy theory: that Netflix been pressured by content makers (in turn egged on by local rights holders like Sky TV) to block foreign users. (Offshore users employ software like Unblock-us to beat Netflix' geo-blocking. They still pay Netflix' monthly fee, and Hollywood Studios get a cut of that — but the theory goes the content makers figure they earn more from selling to local distribution/broadcast rights holders like Sky TV in NZ).

I put the question to Unblock-us: Is Netflix itself responsible for NZ users problems?

In short, yes, but not intentionally.

Unblock-us' Mer Xiao tells NBR that Netflix made a technical change which caught several NZ ISPs on the hop.

The ISPs in question now need to tweak their transparent caching setup (which checks to see if a requested file has already been stored to a server. When it's working properly, it speeds things up).

Will they bother? It seems they would be well advised. The breadth of complaints indicates there's a whole heap of NZ Netflix users — and they'll all be on juicy high-end plans.

NBR has queries in with several affected ISPs, including the biggies (Telecom, Vodafone and Slingshot). Stay tuned.

UPDATE I : Slingshot spokesman Quentin Reade says: "We made some successful changes yesterday with more to come to ensure all devices and browsers are working ... Some devices such as smart TVs are still being worked on." A keen Netflix viewer on Slingshot, who had previously complained to NBR, says the changes have done the trick.

Telecom spokesman Richard Llewellyn says, "We’re currently investigating this with providers to get confirmation, and will arrange for any reconfiguration changes as recommended."

UPDATE II: Customers on all affected ISPs now report normal Netflix transmission.

RAW DATA: Unblock-us statement

We don't believe that this is Netflix blocking foreign users.

We've investigated the issue and here is what we've found:

1. Netflix recently changed the format of URLs for US and Canadian CDN [content delivrery network] used for video streaming

2. The affected NZ providers are using transparent caching proxies for the Netflix CDN range of IP addresses. 

They are NOT using these for other IP ranges we tested.

3. The affected NZ providers are using transparent caching proxies that are set up incorrectly:

- They cache content with "no cache" directive in HTTP header (Pragma: no-cache & Cache-Control: no-store)

- They ignore query string part of the URL for caching

The combination of 1, 2 and 3 has resulted in the Netflix streaming issue. Netflix has started using query string part of the URL to request the movie pieces.

Since the content is cached incorrectly, the Netflix player tries to get a fragment of the movie but gets a completely different movie piece from the proxy and shows the error message. 

Affected ISPs have to reconfigure their proxies to: 

  • Take query string into account OR 
  • Respect "no cache" directive OR 
  • Turn them off for Netflix CDN IP range as caching Netflix streaming does not provide any benefit to the ISP.
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