Tor clients need 4 routers when connecting via IPv6, but only 3 using IPv4
The minimum number of routers in an IPv4-only Tor network is 3. But when a client is using IPv6, that goes up to 4, with the following log message:
Sep 06 13:27:47.000 [info] new_route_len: Not enough acceptable routers (3/4). Discarding this circuit.
Why is one router considered unacceptable? Is this another instance of legacy/trac#19989 (moved)? (One of these routers is an exit.)
This can be tested using chuntney's client-ipv6-only network.