The sctp code doesn't use sk->sk_ipv6only (which is initialised from net.ipv6.bindv6only) but instead uses its own flag sp->v4mapped which always defaults to 1. There may also be an expectation that [gs]etsockopt(sctp_fd, IPPROTO_IPV6, IPV6_V6ONLY,...) will access the flag that sctp uses internally. (Matching TCP and UDP.) Patch is trivial (remembering the inverted state) but I don't have a clean enough source tree :-( David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
