[tor-bugs] #33238 [Core Tor/Tor]: Prop 312: 3.2.3. Use Local Interface IPv6 Address

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#33238: Prop 312: 3.2.3. Use Local Interface IPv6 Address
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     Reporter:  teor            |      Owner:  teor
         Type:  enhancement     |     Status:  assigned
     Priority:  Medium          |  Milestone:  Tor: 0.4.4.x-final
    Component:  Core Tor/Tor    |    Version:
     Severity:  Normal          |   Keywords:  prop312, ipv6
Actual Points:                  |  Parent ID:  #33049
       Points:  1               |   Reviewer:
      Sponsor:  Sponsor55-must  |
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 Make relays (and bridges) use publicly routable addresses
 from the OS interface addresses or routing table, as their IPv4 and IPv6
 addresses.

 Tor has local interface address resolution functions, which support most
 major OSes. Tor uses these functions to guess its IPv4 address. We propose
 using them to also guess tor's IPv6 address.

 We also propose modifying the address resolution order, so interface
 addresses are used before the local hostname. This decision is based
 on our principles: interface addresses are local, trusted, and reliable;
 hostname lookups may be remote, untrusted, and unreliable.

 If the local interface addresses are unavailable, tor opens a UDP socket
 to
 a publicly routable address, but doesn't actually send any packets.
 Instead, it uses the socket APIs to discover the interface address for the
 socket. (UDP is used because it is stateless, so the OS will not send any
 packets to open a connection.)

 Tor already ignores private IPv4 interface addresses on public relays. We
 propose to also ignore private IPv6 interface addresses.

 See proposal 312, section 3.2.1, general case:
 https://gitweb.torproject.org/torspec.git/tree/proposals/312-relay-auto-
 ipv6-addr.txt#n359

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33238>
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