> On 7 September 2020, at 13:57, Michael Tuexen > <michael.tue...@lurchi.franken.de> wrote: > >> 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.
Perhaps I am not understanding this completely, but I believe that it requires UDP encapsulation which is mostly user land code. Thus there would be two implementations of SCTP in the system. I don't think that is the best approach. >> >> 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 That would simplify my code so I am going to implement it. Thanks. >> >> Was this difference intended, or is it likely to change in the future? > I think it is intended. I had a feeling that would be the case, but I would think consistency would be more helpful to those using the services. > > 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"
