Re: socket api problem: can't bind an ipv6 socket to ::ffff:0.0.0.0

Felix von Leitner wrote:

quoted

I don't think this ever worked on Linux, from the very beginning of inet6_bind():

quoted

        /* Check if the address belongs to the host. */
        if (addr_type == IPV6_ADDR_MAPPED) {
                v4addr = addr->sin6_addr.s6_addr32[3];
                if (inet_addr_type(net, v4addr) != RTN_LOCAL) {
                        err = -EADDRNOTAVAIL;
                        goto out;
                }
        } else {

What is the harm in allowing this?  That way an application ported to
IPv6 can still bind IPv4-only.  Why would it be legal to bind to a
specific IPv4 address but not to all IPv4 addresses?

Please show me a porting guide that even mentions supporting IPv4-only mode
through an IPv6 socket by using this method.  There is none that I know of.

The specific case is a bittorrent tracker.  The code was ported to IPv6,
but since there is so much overhead in storing IPv6 addresses you are
supposed to run two processes, one on the IPv6 address and one on the
IPv4 address (the IPv4 one then does not have overhead).  The sane way
to do this is to bind the IPv6 socket to ::ffff:0.0.0.0 then.  Otherwise
you would need some kind of giant abstraction layer in the application.
And we specifically added the ipv4 mapped addresses so applications
would not need to have a giant abstraction layer.

Did I mention *BSD and OSX allow this?

That was their decision, and it doesn't mean it's the right thing to do.  It
doesn't mean Linux shouldn't change either, but name-calling isn't going to get
you anywhere on this list.

Compare your bittorrent server to Apache, which is probably the most widely-used
server application in the world.  It doesn't do what you're trying to do.  See
http://httpd.apache.org/docs/2.2/bind.html and/or browse the source code.

quoted

So are you trying to get IPv4-only behavior out of this socket?  Seems
like the wrong way to go about it.

Why would you say that?

Because if you want IPv4-only you open an AF_INET socket.  There is no
equivalent to IPv6-only, for example when you open an AF_INET6 socket and set
IPV6_ONLY on it.

-Brian