[tor-bugs] #27490 [Core Tor/Tor]: When ClientPreferIPv6ORPort is set to auto, and a relay is being chosen for a directory or orport connection, prefer IPv4 or IPv6 at random

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#27490: When ClientPreferIPv6ORPort is set to auto, and a relay is being chosen for
a directory or orport connection, prefer IPv4 or IPv6 at random
--------------------------+------------------------------------
 Reporter:  neel          |          Owner:  neel
     Type:  enhancement   |         Status:  merge_ready
 Priority:  Medium        |      Milestone:  Tor: 0.3.6.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  ipv6          |  Actual Points:
Parent ID:  #17835        |         Points:
 Reviewer:  teor          |        Sponsor:
--------------------------+------------------------------------

Comment (by teor):

 Here's what we discussed at the meeting:

 Pathbias isn't affected, because it only triggers after two hops.

 Guard selection may be affected, but:
 * IPv4-only clients will try 1-2 guards, and fail 0-1 times before
 connecting on average (all guards have IPv4)
 * IPv6-only clients will try 1-5 guards, and fail 0-5 times before
 connecting on average (20% of guard weight has IPv6 -
 https://metrics.torproject.org/advbw-ipv6.html )
 We think this is acceptable, and if it causes bugs in the guard code,
 let's fix the guard code.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27490#comment:21>
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