On 21/04/2020 23:45, Michael Tuexen wrote: >> Looks like the failing call is here: >> >> if (setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, >> (const void *)&on, sizeof(on)) != 0) { > Can you provide a pointer to the code? Yes, its here: https://github.com/openssl/openssl/blob/fa555aa8970260c3e198d91709b2d4b3e40f8fa8/crypto/bio/b_sock2.c#L267-L282 Matt