Re: [javagroups-users] Handling of IPv6 mcast_addrs

[Vladimir B. <vbl...@re...>]

I agree with your proposal and I think Mr. Andiamo would agree as well :)

On 09-10-27 12:28 PM, Bela Ban wrote:
> In 2.8, we changed the way IP addresses are handled. Below, I want to
> briefly describe an issue I ran into, and the corresponding fix, but
> wanted to solicit feedback, as this will change things a bit.
>
> The type of a stack (IPv4, IPv6 or dual) is determined by the installed
> stacks and the system props java.net.preferIPv4Stack (default: false)
> and java.net.preferIPv6Addresses (default: false).
>
> #1 If only preferIPv4Stack is set, then we use IPv4.
>
> #2 If only preferIPv6Addresses is set, we use IPv6.
>
> #3 If both are set, we use IPv4.
>
> #4 If neither is set, we use IPv6 (!)
>
>
> Now if we have a config such as
>
> CONFIG-1:<UDP mcast_addr="232.5.5.5" ... />  // IPv4 mcast_addr
> CONFIG-2:<UDP mcast_addr="ff0e::8:8:8" ... />  // IPv6 mcast_addr
>
> , then the following can happen (assuming we have both types of stack
> available):
>
> We run without any java.net.preferXXX props:
>
>      * The stack is IPv6 by default
>      * CONFIG-1 will fail because we passed an IPv4 address to an IPv6 stack
>
> We run with preferIPv4Stack=true:
>
>      * The stack is IPv4
>      * CONFIG-2 will fail as we're running with an IPv4 stack
>
> Both props are set:
>
>      * CONFIG-2 will fail, same as above
>
> *So my proposal is to remove all properties from the shipped XML
> configurations that have IP addresses, e.g. bind_addr (not used anywhere
> though) and UDP.mcast_addr.*
>
> This will allow for the case where no java.net.preferXXX props are set;
> it will not fail (it currently does fail !) because we're picking a
> stack type compliant (IPv6) mcast_addr.
>
> I assume a lot of folks trying out JGroups for the first time don't
> bother even reading the documentation and will *not* set a
> java.net.preferXXX system property, and would therefore run into an
> exception when using a current sample config file, e.g. udp.xml. This
> won't happen with the proposed change.
>
> Folks who want to force a specific stack type and use specific IP
> addresses, have to (1) define the right values in the XML config (or
> pass them to JGroups via system props) and (2) possibly set a
> java.net.preferXXX system property (not needed if the default is what a
> user wants).
>
> What do people think ? Feedback appreciated !
>
>
>