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.
