IP networking single socket, both IPv4 and V6?

[Karl Denninger]

On 1/4/2018 10:32, Lewis Donzis wrote:
> On Jan 4, 2018, at 10:17 AM, Karl Denninger <karl at denninger.net> wrote:
>> I've written a fair bit of code that binds to both Ipv4 and v6 for
>> incoming connections, using two sockets (one for each.)
>>
>> Perusing around the 'net I see an implementation note written by IBM
>> that implies that on their Unix implementation you can set up an INET6
>> listener and it will open listeners on *both* IPv4 and v6; you code it
>> as an Ipv6 socket/bind/listen/accept, and if an Ipv4 connection comes in
>> you get a prefix'd IPv4 address back when you call getpeername().
>>
>> This would obviously shorten up code and remove the need to open the
>> second listener socket, but playing with this on FreeBSD it doesn't
>> appear to work -- I only get the IPv6 listener in "netstat -a -n"
>> showing up and as expected a connection to a v4 address on that port
>> fails (refused, since there's no listener.)
>>
>> Is this something that *should* work on FreeBSD?
> It works.  We do it all the time.  You either have to set the sysctl:
>
>    net.inet6.ip6.v6only=0
>
> which you can do in /etc/sysctl.conf or with the sysctl utility, or, in your program, use setsockopt to turn off the V6ONLY option, e.g.:
>
>    setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof (int)); // Turn off v6-only
>
> We use the first method, which is broken in FreeBSD 11.1 prior to patch level 5 or 6, I can’t remember which, but works in all others.  The second method is considered to be more portable.
>
> FWIW, Linux, by default, sets v6only off, so it doesn't require anything special.
>
Well that explains why it didn't work as expected... thanks :-)

-- 
Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4897 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://lists.freebsd.org/pipermail/freebsd-net/attachments/20180104/fc7ff9f3/attachment.bin>