netdev - Re: /128 link-local subnet on 6in4 (sit) tunnels?

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Message-ID: <20130328131212.GA7721@order.stressinduktion.org>
Date:	Thu, 28 Mar 2013 14:12:12 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Wilco Baan Hofman <wilco@...nhofman.nl>
Cc:	netdev@...r.kernel.org, YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Subject: Re: /128 link-local subnet on 6in4 (sit) tunnels?

On Thu, Mar 28, 2013 at 02:00:38PM +0100, Wilco Baan Hofman wrote:
> For 6rd, rfc5969 section 9 specifies that a link *may*, if needed, have
> a non-used link-local address [2], this may be where the /128 comes in:
> 
>    The 6rd link is modeled as an NBMA link similar to other automatic
>    IPv6 in IPv4 tunneling mechanisms like [RFC5214], with all 6rd CEs
>    and BRs defined as off-link neighbors from one other.  The link-local
>    address of a 6rd virtual interface performing the 6rd encapsulation
>    would, if needed, be formed as described in Section 3.7 of [RFC4213].
>    However, no communication using link-local addresses will occur.
> 

Hm, perhaps this is the reason. Also, RFC3964 ("Security Considerations for
6to4") states that the use of non-global addresses on a 6to4 link should be
prohibited:

|   o  Disallow traffic in which the destination IPv6 address is not a
|      global address; in particular, link-local addresses, mapped
|      addresses, and such should not be used.

Could you check if the creation of a /128 ll address does act as a guard
against that and does suppress ll traffic? I am not sure.

Perhaps a patch where we check the IFF_POINTTOPOINT flag and selectively
create a /128 or /64 would be a solution.

Thanks,

  Hannes
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