[tor-bugs] #29570 [Core Tor/Tor]: Enforce mutually exclusive logic for IPv6 ORPort flags

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#29570: Enforce mutually exclusive logic for IPv6 ORPort flags
-------------------------------------------------+-------------------------
 Reporter:  s7r                                  |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:  Tor:
                                                 |  unspecified
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-relay, ipv6, reachability,       |  Actual Points:
  needs-proposal                                 |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Changes (by teor):

 * keywords:  tor-relay, ipv6, reachability => tor-relay, ipv6,
     reachability, needs-proposal


Comment:

 I can see a good argument for reducing the size of the consensus.

 The argument for making connections direct is not very strong, because tor
 already supports NAT using the NoListen/NoAdvertise flags.

 I can also see a good argument for allowing operators to configure their
 relays the way that they want:
 > a relay in an IPv6 only network that is through router tricks still
 reachable on a IPv4 address seems a sensible case to me.

 The argument for using a pluggable transport instead of an IPv6 redirect
 is not very strong, because that needs extra client configuration.

 Let's take a step back:

 Here are our goals:
 1. support IPv4 and IPv6
 2. encourage more IPv6 relays
 3. make the votes efficient for authorities to create
 4. make the consensus efficient for clients to download
 5. make relay connections efficient
 6. make Tor easy to maintain

 Allowing an IPv4 and an IPv6 advertised address to redirect to the same
 underlying port:
 * makes 1 and 2 better for a few relays
 * makes 3, 4, and 5 slightly worse, all over the network

 Rejecting this rare case:
 * makes 1 and 2 worse for a few relays
 * makes 3, 4, and 5 slightly better, all over the network
 * makes 6 a tiny bit worse, because it requires a little bit of extra code
 and documentation

 Adding a special flag or option for this rare case:
 * makes 1 and 2 better for a few relays
 * makes 3, 4, and 5 slightly worse, all over the network
 * makes 6 worse all the time, because extra flags and options need code
 and tests and documentation

 Tor uses a proposals process to make design decisions like this.
 Here is our proposals process:
 https://gitweb.torproject.org/torspec.git/tree/proposals/001-process.txt

 A good proposal will talk about the alternative designs, and give reasons
 why each design would be better or worse for tor users, relay operators,
 and the tor network.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29570#comment:9>
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