[lug] sendto(2) problem with ipv4/ipv6 addresses...

Zan Lynx zlynx at acm.org
Mon Apr 2 12:55:06 MDT 2012

On Mon, 2012-04-02 at 12:38 -0600, Alan Robertson wrote:
> As part of the Assimilation Monitoring project (assimmon.org), I've
> been writing some UDP network code to send packets.  It seems to work
> fine when sending to the ipv6 loopback address (::1), but not when
> sending to ipv4 addresses.  I'm sending to ipv4 addresses by using the
> ipv4 part of the ipv6 address space ("::ffff:aa.bb.cc.dd").  Tcpdump
> is showing that nothing is being sent - so the kernel is blocking this
> call before it goes out.

I believe that using IPv4 addresses mapped in IPv6 requires a gateway
device to convert the protocol from IPv6 to IPv4. This seems to be
called NAT-PT.

Here is one source I Googled that describes configuring it on Linux:

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