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

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

[Roy Marples]

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Hi

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.

Thanks

Roy

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This allows userland to set a possibly different link-local address
like say one based on RFC7217.

Signed-off-by: Roy Marples <roy@marples.name>

--- net/ipv6/addrconf.c.orig	2014-08-10 19:39:50.377073417 +0000
+++ net/ipv6/addrconf.c	2014-08-10 20:19:03.139002051 +0000
@@ -2751,6 +2751,11 @@ static void addrconf_dev_config(struct n
 	if (IS_ERR(idev))
 		return;
 
+	/* If we already have a link-local address, don't bother
+	 * adding a new one. */
+	if (ipv6_get_lladdr(dev, &addr, 0) == 0)
+		return;
+
 	memset(&addr, 0, sizeof(struct in6_addr));
 	addr.s6_addr32[0] = htonl(0xFE800000);
 

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

[Hannes Frederic Sowa]

Hi,

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.

Bye,
Hannes

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

[Roy Marples]

Hi

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.

Roy

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

[Hannes Frederic Sowa]

On Mo, 2014-08-11 at 00:05 +0000, Roy Marples wrote:
> Hi
> 
> 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

Bye,
Hannes

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

[YOSHIFUJI Hideaki]

Hello.

Roy Marples wrote:
> Hi
>
> 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.

Well, I think this is incomplete, for example, we will continue generating
global address from eui64.

I think we should implement such functionality through "if token" bits.

--yoshfuji

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

[Roy Marples]

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

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

[Jiri Pirko]

Mon, Aug 11, 2014 at 11:22:04PM CEST, roy@marples.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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