Re: [jgroups-dev] JGroups preference for IPv6

OK, in an IPv6 *only* stack, an *IPv4* class D (multicast) address 
cannot get mapped to an IPv4 mapped IPv6 address. This works fine for 
unicast addresses.

I have to verify that, if you have a dual stack, an IPv4 multicast 
address can co-exist with IPv6 addresses.



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

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