TTL ignored when sending Multicast UDP Datagram to IPv4 address via IPv6 socket

[Don Coleman]

-Djava.net.preferIPv4Stack=true works fine for IPv4, but my
application needs to send both IPv4 and IPv6.

I'd be interested to see Edward Wang's patch for this issue.

On 6/1/07, Alan Bateman <Alan.Bateman at sun.com> wrote:
> Don Coleman wrote:
> > I'm have a problem setting TTL when sending Multicast packets to an
> > IPv4 address over an IPv6 socket.
> >
> > Setting the TTL in Java has no effect when sending to an IPv4 address.
> > It is always 1.
> >
> > This is only a problem on Linux, it works fine on OS X, Solaris and
> > Windows.
> >
> > This problem exists with JDK5, but it looks like it's also in the JDK7
> > code.
> >
> > https://openjdk.dev.java.net/source/browse/openjdk/jdk/trunk/j2se/src/solaris/native/java/net/PlainDatagramSocketImpl.c?annotate=237
> >
> >
> > on line 1873 IPV6_MULTICAST_HOPS is set
> > for Linux I think we need also need to set IP_MULTICAST_TTL
> >
> > I've attached sample Java and C code that demonstrates the problem
> > here https://bugs.launchpad.net/ubuntu/+bug/112257
> >
> > Any thoughts if this is a Java problem or a Linux kernel bug?
> The bug tracking this one is:
>     http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6250763
>
> At least in older kernels, it wasn't possible to set IPv4 multicast
> options on IPv6 sockets (the setsockopt would fail). Edward Wang has
> been testing with recent kernels and has results that suggest that
> setting the IPv4 options work now. I believe he has a fix/patch in the
> works to address this (Edward - can you comment?).
>
> If you need a workaround then run with -Djava.net.preferIPv4Stack=true
> so that all sockets are IPv4 (even if the machine has IPv6 enabled).
>
> -Alan.
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