We can work on this ticket now, but we should do the code movement in legacy/trac#33789 first. Make relays and bridges use the Address torrc option to find their IPv6 addresses. This ticket covers the IPv6 literal case: 1. Explicit IP addresses: * allow the option to be specified up to two times, * use the IPv4 address for IPv4, * use the IPv6 address for IPv6. Configuring two addresses in the same address family is a config error. 2. Hostnames / DNS names: * allow the option to be specified up to two times, * look up the configured name, * use the first IPv4 and IPv6 address returned by the resolver, and Resolving multiple addresses in the same address family is not a runtime error, but only the first address from each family will be used. It is an error to configure an Address option with a private IPv4 or IPv6 address. (If tor is configured with a custom set of directory authorities, private addresses should be allowed, with a notice-level log.) See proposal 312, section 3.2.1, case 1: https://gitweb.torproject.org/torspec.git/tree/proposals/312-relay-auto-ipv6-addr.txt#n252 As soon as we implement this ticket, we should implement legacy/trac#33246 to automatically open an IPv6 ORPort based on the Address config. (Or any discovered addresses.) Then we should test the different IPv4/IPv6 configs listed in legacy/trac#33235.