Prop 312: 3.2.1. Test Address torrc Option Configurations
We should support the following combinations of address literals and hostnames:
- (A) No configured Address option
- (B) Address IPv4 literal
- (C) Address hostname (use IPv4 and IPv6 DNS addresses)
- (D) Address IPv6 literal
- (E) Address IPv4 literal / Address IPv6 literal
- (F) Address hostname / Address hostname (use IPv4 and IPv6 DNS addresses)
- (G) Address IPv4 literal / Address hostname (only use IPv6 DNS addresses)
- (H) Address hostname (only use IPv4 DNS addresses) / Address IPv6 literal
If we can't find an IPv4 or IPv6 address using the configured Address options:
- No IPv4: guess IPv4, and its reachability must succeed.
- No IPv6: guess IPv6, publish if reachability succeeds.
Combinations A and B are the most common legacy configurations. We want to support the following outcomes for all legacy configurations:
- automatic upgrades to guessed and reachable IPv6 addresses,
- continuing to operate on IPv4 when the IPv6 address can't be guessed, and
- continuing to operate on IPv4 when the IPv6 address has been guessed, but it is unreachable.
See proposal 312, section 3.2.1, testing notes: https://gitweb.torproject.org/torspec.git/tree/proposals/312-relay-auto-ipv6-addr.txt#n270