netdev - Re: [PATCH net-next] ipv6, token: allow for clearing the current device token

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Date:	Fri, 8 Apr 2016 17:36:22 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	Daniel Borkmann <daniel@...earbox.net>, davem@...emloft.net,
	robbat2@...too.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ipv6, token: allow for clearing the current
 device token

On 08.04.2016 17:25, Bjørn Mork wrote:
> Hannes Frederic Sowa <hannes@...essinduktion.org> writes:
>
>> On Fri, Apr 8, 2016, at 16:18, Bjørn Mork wrote:
>>> Daniel Borkmann <daniel@...earbox.net> writes:
>>>
>>>>
>>>>   	if (!token)
>>>>   		return -EINVAL;
>>>> -	if (ipv6_addr_any(token))
>>>> -		return -EINVAL;
>>>>   	if (dev->flags & (IFF_LOOPBACK | IFF_NOARP))
>>>>   		return -EINVAL;
>>>
>>> Not directly related to the patch in question.  It just made me aware of
>>> this restriction...
>>>
>>> I realize that I'm a few years late here, but what's with the IFF_NOARP?
>>> Is that just because we can't do DAD for the token based addresses?  How
>>> is that different from manually configuring the whole address?
>>
>> IFF_NOARP is kind of the equivalent to no neighbor discovery. If you set
>> a token and never get in a router advertisement you never create a
>> tokenized ip address, thus the feature is useless.
>
> You can get router advertisements with IFF_NOARP. You cannot lookup L2
> addresses, but the L3 prefix info is still as useful as with any other
> interface.

Of course router advertisements can be send and received with IFF_NOARP 
and probably we act on them as usual, as you showed. Looking in the 
source we don't really specify what those flags mean/do for IPv6. So I 
think you can assume that it is in there because of history.

I would absolutely not mind if you remove the limitation for IFF_ARP.

Bye,
Hannes