netdev - Re: [PATCH] ipv6: do not add link-local address if one already exists

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Date:	Mon, 11 Aug 2014 22:22:04 +0100
From:	Roy Marples <roy@...ples.name>
To:	Hannes Frederic Sowa <hannes@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: do not add link-local address if one already exists

Hi

On 2014-08-11 01:11, Hannes Frederic Sowa wrote:
> On Mo, 2014-08-11 at 00:05 +0000, Roy Marples wrote:
>> On 2014-08-10 20:37, Hannes Frederic Sowa wrote:
>> > On So, 2014-08-10 at 19:56 +0000, Roy Marples wrote:
>> >> Currently the kernel will always add an IPv6 link-local address
>> >> based on the hardware address when the interface is brought up.
>> >> This is probably based on the assumption that userland would
>> >> never add one before the interface is brought up.
>> >>
>> >> However, one at least one userland application (dhcpcd) does this so
>> >> it can implement RFC7217 which can be used for link-local addresses
>> >> as well.
>> >>
>> >> Attached is a patch which checks to see if a link-local address exists
>> >> before indiscriminately adding one.
>> >
>> > Please have a look at:
>> > https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/commit/?id=bc91b0f07ada5535427373a4e2050877bcc12218
>> >
>> > This was recently implemented just for this specific case.
>> 
>> Is that tunable available in /proc or /sys?
>> I'm not overly keen on adding a netlink call just for that in dhcpcd, 
>> it
>> would be a lot of bloat compared to the kernel patch.
> 
> Can you call iproute via a script? Would that fit your needs?
> https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/commit/?h=net-next&id=ff7c20844049be836c10087cb2418b99ff36ca2b

Not really as there is no guarantee iproute2 is installed on the host.
For now, I've added a netlink call at the expense of around 400 bytes.

Thanks

Roy
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