libzmq's IPv6 support is buggy when also using DNS hostname: in
particular, if you try to connect to a DNS name that has an IPv6
address, then zmq will only try an IPv6 connection, even if the local
client has no IPv6 connectivity, and even if the remote is only
listening on its IPv4 address.
libzmq's IPv6 support is buggy when also using DNS hostname: in particular, if you try to connect to a DNS name that has an IPv6 address, then zmq will only try an IPv6 connection, even if the local client has no IPv6 connectivity, and even if the remote is only listening on its IPv4 address.
This is much too unreliable to enable by default.