Re: DHCPv6, IPv6 net tools

From: Jeroen Massar
Date: Mon Feb 05 2007 - 18:28:12 EST

David W. Hankins wrote:
> On Mon, Feb 05, 2007 at 01:40:03PM -0800, David W. Hankins wrote:
>> ifconfig foo0 inet6 down
>> ifconfig foo0 inet6 up
> Wouldn't you know it, just when I've given up searching for a
> solution and resorting to asking someone, I find my answer in
> /sbin/ip.

ip is the cool tool indeed ;)
Unfortunately it is also one of the few locations to find
'documentation' about these interfaces.

>> While I'm asking on this subject, DHCPv6 introduces the concept of
>> a 'preferred' lifetime. The objective is to encourage applications
>> to move from an old address to a new one over a grace period before
>> the old address fully expires.
>> Have either the linux kernel or net-tools folks spent any time
>> thinking about how this will be implemented and signalled? I'm
>> not seeing anything related in the ifconfig manpage.

The address which is the 'most preferred' will be used when creating a
new outbound connection when the application didn't forcefully bind to a
specific address.

When an address becomes deprecated it just keeps on being used by the
application. No transition to another address is done. Only thing is
that it won't be used for creating new connections.

Afaik there is indeed no signaling for this yet. But it is tricky anyway
to have new-interface/address detection in a unix-wide way. One tends to
end up listening to routing messages of the kernel interface; which
IMHO is a bit much to ask from applications.

From that perspective, for C, there should have been a layer between the
normal BSD socket calls and the application user ages ago which handled
these scenarios.


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