Is it possible to make this optional? Ideally, on per-torrent basis, but at least a flag in advanced options would be fine. First, there's a security issue. Some bad client in swarm could report some random IPv6 address, thus poisoning swarm and making it connect to this address which could be a kind of DDoS, since other clients cannot validate such IPs. Same trick could be done by PEX, but this one will work even on torrents with private flag set. Another reason is if I want to communicate on IPv6 only. I know I can block all IPv4 range by ipfilter.dat but what if I don't want my IPv4 address exposed at all? When this advanced flag is set maybe uTorrent should ignore other addresses it receives from other peers during handshake. This will work like a kind of VPN that would totally hide my IPv4 address from anyone for privacy reasons.