Re: [jgroups-dev] JGroups preference for IPv6

This won't work: even though you *could* have a dual stack, unless you 
set one of the java.net.preferXXX flags, the JVM picks an IPv6 stack by 
default !

So a class D IPv4 address, e.g. 239.5.5.5, will fail the creation of the 
MulticastSocket in UDP (cannot bind to 239.5.5.5), and we're back to 
having promiscuous traffic.

However, what could be done to solve the problem of using IPv4 class D 
addresses within an IPv6 stack is to map the IPv4 multicast addresses to 
IPv6 multicast addresses by prepending an IPv6 /96 prefix, e.g.

239.5.5.5 --> FF0e::239.5.5.5, as outlined in [1]. The prefix <FF0e::> 
could be hard coded, for instance.

I might want to issue a warning though because the transformation might 
not end up resulting in an IPv6 multicast address of the type a user 
wants... OTOH, this is already done for unicast addresses...

WDYT ?


[1] 
http://www.6net.org/publications/standards/draft-venaas-mboned-v4v6mcastgw-00.txt
[2] http://www.faqs.org/rfcs/rfc2529.html



Brian Stansberry wrote:
> This is somewhat related to previous discussion at [1] and related 
> JGRP-1152 [2].
>
> Since we've upgraded JBoss AS trunk to JGroups 2.10.0.Alpha3, it will 
> no longer start on a machine that supports both IPv4 and IPv6. This is 
> because we don't specify java.net.preferIPv4Stack in our startup 
> scripts, so Util.getIpStackType() returns StackType.IPv6. But we 
> configure IPv4 multicast addresses by default so the JGRP-1152 check 
> fails the startup.
>
> Since we're specifying IPv4 addresses by default, perhaps our startup 
> scripts could set -Djava.net.preferIPv4Stack=true. Jason can comment 
> if he likes; it may be necessary although I don't really like it (yet 
> another config in an obscure location).
>
> I'm wondering if JGroups can handle this situation more flexibly. I've 
> attached an *untested* patch that shows what I was thinking:
>
> 1) Add a new StackType.Either which Util.getIpStackType() returns if 
> the OS supports both stack types and no java.net.preferXXX property is 
> set.
>
> 2) Configurator.setupProtocolStack() recognizes StackType.Either and 
> when it's analyzing the InetAddresses it's seeing, it uses the first 
> one it sees to switch to either StackType.IPv4 or StackType.IPv6. So 
> in this case the users choice of addresses controls the behavior.
>
> 3) Thereafter, the normal JGRP-1152 checks apply, so illegal 
> inconsistencies are caught and rejected.
>
> I checked for other uses of Util.getIpStackType() and tweaked the one 
> that needed it to deal with a return value of StackType.Either. I 
> haven't checked *all* uses of StackType though; wanted to get some 
> feedback first.

-- 
Bela Ban
Lead JGroups / Clustering Team
JBoss

------------------------------------------------------------------------------
Download Intel&#174; Parallel Studio Eval
Try the new software tools for yourself. Speed compiling, find bugs
proactively, and fine-tune applications for parallel performance.
See why Intel Parallel Studio got high marks during beta.
http://p.sf.net/sfu/intel-sw-dev
_______________________________________________
Javagroups-development mailing list