[tor-bugs] #33224 [Core Tor/Tor]: Prop 311: 4.3.2. Add AssumeIPv6Reachable Option

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#33224: Prop 311: 4.3.2. Add AssumeIPv6Reachable Option
---------------------------+------------------------------------
 Reporter:  teor           |          Owner:  teor
     Type:  enhancement    |         Status:  assigned
 Priority:  Medium         |      Milestone:  Tor: 0.4.4.x-final
Component:  Core Tor/Tor   |        Version:
 Severity:  Normal         |     Resolution:
 Keywords:  ipv6, prop311  |  Actual Points:
Parent ID:  #33221         |         Points:  1
 Reviewer:                 |        Sponsor:  Sponsor55-must
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Comment (by teor):

 This ticket is optional, but there are some risks if we don't implement
 it.

 Here are the risks and mitigations:

 Don't implement the AssumeIPv6Reachable torrc option:
 * Low Risk
 * Issue:
   * Operators can't disable IPv6 self-tests, but continue using IPv4
     self-tests.
 * Workaround:
   * Operators use AssumeReachable to disable IPv4 and IPv6 self-tests.

 Don't implement the AssumeIPv6Reachable consensus parameter:
 * Medium Risk
 * Issue:
   * If there is a network-wide issue with IPv6 self-tests, all IPv6
     relays (30%) and bridges (unknown percentage) will go down.
 * Workaround:
   * There is no workaround.
 * Mitigation:
   * Make sure chutney fails when relay and bridge reachability
     self-tests fail. Chutney ensures relay self-tests work, but
     doesn't check bridges. There are two alternative ways to do
     bridge checks:
     * Fix tor bridge descriptor uploads (#33582) and check them in
       chutney (#33407), or
     * Make chutney check tor's logs for reachability self-tests
       (#34037).

 If we implement the consensus parameter, we should also implement the
 torrc option, so operators can configure the option independently.

 Since this option stops relays publishing their descriptors, we should
 probably test it in chutney, or on the public tor network. (See #33229 and
 #33230.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33224#comment:1>
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