> On 7. Sep 2020, at 22:48, Doug Hardie <bc...@lafn.org> wrote: > > I was quite surprised to discover that the sockaddr structure returned from > recv_fd and recvfrom handle IPv4 addresses differently when using an INET6 > socket. I don't know if this was intended, or a side effect. I started > using SCTP because of the need for accessing multi-homed servers. Some would > be on IPv6 and others on IPv4. SCTP handles that nicely if you use an INET6 > socket. When a transaction is received, if it is to an IPv4 address, then > the returned sockaddr will have a inet_family of IPv4 and the IPv4 structure. > If it was sent to an IPv6 address, then the inet6_family is used. A simple > test of the family tells you which address format was provided and the > address is in IPv4 or IPv6 format accordingly. > > However, A new site needed to be added and it is behind a NAT router. The > problem with SCTP is that most (possibly all) NAT routers only work with TCP > and UDP. They will not port forward SCTP. So I have no way to get through > to the machine. So I added code to check for that situation and use UDP > instead. This will work because I don't thing it is at all likely that a > machine behind NAT can be multi-homed. Would using SCTP/UDP/IPv[46] be an option? It is supported by the FreeBSD kernel. See https://tools.ietf.org/html/rfc6951#section-6 for the socket API for it. > > However, the code to obtain the remote IP address failed miserably. It turns > out that if you have v6only set to 1, you will never see the IPv4 packets. > If you set it to 0, then you get the packets, but the sockaddr format with > UDP is different than that for SCTP. If it is an IPv6 address, everything is > the same. However, if it is an IPv4 address, then the family remains IPv6, > and the address is in sin6_addr and it is in the format ::ffff:n.n.n.n. This > makes it interesting as I need to obtain the IPv4 address as part of the > verification process that the transaction is authorized. For UDP and TCP you always get IPv6 addresses on AF_INET6 sockets. If you are actually using IPv4, IPv4-mapped IPv6 addresses are used. For SCTP you an choose if you want IPv4-mapped IPv6 addresses or IPv4 address. It is controlled by the socket option specified in https://tools.ietf.org/html/rfc6458#section-8.1.15 > > Was this difference intended, or is it likely to change in the future? I think it is intended.
Best regards Michael > > -- Doug > > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" _______________________________________________ freebsd-net@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
