[tor-bugs] #33880 [Core Tor/Tor]: Confusing "Your relay has a very large number of connections to other relays" relay message

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#33880: Confusing "Your relay has a very large number of connections to other
relays" relay message
------------------------------+--------------------
     Reporter:  arma          |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------
 A new relay operator reports this complaint in their logs, showing up
 hourly:
 {{{
 Your relay has a very large number of connections to other relays. Is your
 outbound address the same as your relay address? Found 13 connections to 8
 relays. Found 13 current canonical connections, in 0 of which we were a
 non-canonical peer. 5 relays had more than 1 connection, 0 had more than
 2, and
 0 had more than 4 connections.
 }}}

 I checked, and their outbound address was the same as their relay address.

 Upon investigation, it looks like the redundant connections are to
 directory authorities.

 My theory is that the change from #17592 (which went into 0.3.1.1-alpha,
 commit d5a151a0) is responsible: while before that canonical relay-to-
 relay connections would expire after either side first reached its
 randomized "15 to 22.5 minute" timeout, now they expire after either side
 reaches its "45 to 75 minute" timeout. And since directory authorities
 test reachability every 1280 seconds (around 21.3 minutes), that means it
 is expected that most relays will have duplicate canonical connections
 with directory authorities.

 Possible fixes:

 (A) Change the notice-level log to make it clearer that it's not scary, or
 at least it's not actionable. Maybe that means making it info-level so
 nobody will see it. Probably not the best option, assuming there *are*
 cases where we do want relay operators to hear it.

 (B) In channel_check_for_duplicates(), change
 {{{MIN_RELAY_CONNECTIONS_TO_WARN 5}}} to a high enough number that even if
 we have 2 canonical conns per authority, plus a bit more, the log message
 still doesn't trigger.

 (C) In channel_check_for_duplicates(), skip over connections to directory
 authorities in some way, since we know they will be special.

 (D) Make connections to or from directory authorities expire quicker, on
 the theory that they don't really need the same level of padding
 protection as other connections.

 (E) Your idea here?

 I'd be fine with any of B,C,D. Whichever one can be done with an easy,
 short, and non-invasive patch is my favorite. Maybe that's "B, raise it to
 30"? That would make the message trigger when we have connections to more
 than 30 relays and also we have more than 45 connections open. Or we could
 pick the more conservative "raise it to 40", on the theory that small
 numbers are more likely to have edge cases and less indicative of major
 network problems anyway.

 And while we're at it, it might be smart to say in the log message what
 action we want the relay operator take, e.g. "Please report:".

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33880>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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