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

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Date:	Wed, 13 Aug 2014 19:10:27 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Roy Marples <roy@...ples.name>
Cc:	Hannes Frederic Sowa <hannes@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: do not add link-local address if one already exists

Mon, Aug 11, 2014 at 11:22:04PM CEST, roy@...ples.name wrote:
>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.

The iface to idev->addr_gen_mode can be certainly added to sysfs. Feel
free to do so.


>
>Thanks
>
>Roy
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