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Re: [tor-bugs] #21394 [Core Tor/Tor]: connection timeouts are affecting Tor Browser usability
#21394: connection timeouts are affecting Tor Browser usability
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Reporter: arthuredelstein | Owner: (none)
Type: defect | Status: new
Priority: Very High | Milestone: Tor:
| 0.3.3.x-final
Component: Core Tor/Tor | Version:
Severity: Normal | Resolution:
Keywords: tbb-performance, tbb-usability, | Actual Points:
performance, tbb-needs |
Parent ID: | Points:
Reviewer: | Sponsor:
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Comment (by Sebastian):
So yes, I think that bugreport is very relevant here. I think this is a
libevent bug/an unfortunate issue with how libevent and unbound interact.
By default libevent only allows 64 DNS requests to be inflight at the same
time. When asking unbound to resolve something and the dns server in
question nullroutes traffic from unbound, it takes longer than named to
reply with a SERVFAIL. (named's timeout matches what Tor uses). So if a
bigger dns server operator decides it has gotten to many queries from a
relay, reaching that limit of 64 inflight queries happens in absolutely no
time and all other DNS requests get queued.
There may be an additional issue where we're marking our local unbound as
down because it didn't reply quickly enough to a query we made, because
it's still trying to answer it. Combined this would easily explain why DNS
gets wedged completely.
We REALLY need a high-volume exit operator to help us debug these
assumptions.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21394#comment:34>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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