[tor-dev] Connections failed to default obfs4 bridges

[David Fifield]

On Wed, Mar 28, 2018 at 10:57:13AM -0400, Rob Jansen wrote:
> In a recent connectivity test to the default obfs4 bridges [0], we found that we are unable to connect to 10 or so of them (from open networks, i.e., no local filtering).
> 
> Is this a feature, like some of them only respond to users in certain parts of the world? Or is this a bug, like the default list of bridges refers to old bridges that are no longer available? Or am I misunderstanding functionality here?

Do you mean 10 distinct IP addresses, or 10 ports on a few IP addresses?
Not all the IP addresses in the list are distinct.

Even while Lynn Tsai, Qi Zhong, and I were closely monitoring default
bridge reachability, a lot of the default bridges were often offline,
because of reboots, iptables problems, etc. See for example the "Orbot
bridges" strip of Figure 5.2 here; the gray and red areas that precede
blocking are where the bridge was simply offline:
https://www.bamsoftware.com/papers/thesis/fifield-thesis.pdf#page=43

We have a lot of past measurements of default bridges. The rows with
site="eecs-login" are from the U.S.
https://www.bamsoftware.com/proxy-probe/ (download the repo, not
probe.csv.gz, which isn't as recent)