[tor-talk] meek-azure was blocked in China for about 4 days

[David Fifield <david@xxxxxxxxxxxxxxx>]

For about four days (January 29 to February 1, 2016), meek-azure was
blocked in China. The blocking may not have been intended for
meek-azure, and may not have been deliberate blocking, but it had the
effect of blocking the service. It is unblocked again since February 2.

The nature of the event seems to be dropping of HTTPS connections to a
specific Azure CDN edge server, cs3.wpc.v0cdn.net, which at the time had
an IP address of 68.232.45.200. Plain HTTP connections were not
affected. The blocking was not DNS blocking of a specific domain name,
nor was it TLS SNI (Server Name Indication) filtering: all domain names
we tried for the IP address failed equally.

Here you can see a history of the event, based on GreatFire.org
measurements. Click on a calendar square for more details. Red is
blocked and orange/green is unblocked.
        https://en.greatfire.org/https/ajax.aspnetcdn.com

On February 2, the domain name changed to a different IP address,
68.232.45.201. That may be what caused the end of the block. I don't
know whether HTTPS connections to the old IP address are still being
dropped in the same way.

It's a good idea to be prepared in case of events like this. Here are
some links on technical ways to work around certain kinds of meek
blocking. (In this case, changing the front domain would have worked
only if you found a name that resolved to a different IP address.)
https://lists.torproject.org/pipermail/tor-talk/2015-January/036410.html
https://trac.torproject.org/projects/tor/wiki/doc/meek#Howtochangethefrontdomain
https://plus.google.com/109790703964908675921/posts/26zCmDmjYXP
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