Re: [v6ops] Extension Headers / Impact on Security Devices

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 27 May 2015 20:29 UTC

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Date: Thu, 28 May 2015 08:29:37 +1200
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: Joe Touch <touch@isi.edu>, Gert Doering <gert@space.net>
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Subject: Re: [v6ops] Extension Headers / Impact on Security Devices
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On 28/05/2015 05:24, Joe Touch wrote:
> 
> 
> On 5/27/2015 12:39 AM, Gert Doering wrote:
>> Hi,
>>
>> On Wed, May 27, 2015 at 12:23:30PM +1200, Brian E Carpenter wrote:
>>>> FWIW, I don't see anything that prohibits adding headers either.
>>>
>>> "With one exception, extension headers are not examined or processed
>>> by any node along a packet's delivery path, until the packet reaches
>>> the node (or each of the set of nodes, in the case of multicast)
>>> identified in the Destination Address field of the IPv6 header."
>>>
>>> To me that clearly implies not adding (which is a form of processing).
>>
>> So how do the SR folks handle that?  From what I heard, the intended
>> deployment really is "inside your administrative domain, SR headers get
>> added, processed, and when the packet leaves your domain, they can be
>> (optionally) removed again to not upset your neighbours"...
> 
> AFAICT, SR headers are destination options, and aren't supposed to be
> modified by anything but the endpoints (where each addressed hop in such
> a route is such an endpoint).
> 
> So I would think that they MUST NOT be added to IPv6 datagrams except by
> the source.

I agree, but I think the SR people prefer to think otherwise, which just
stacks up MTU problems for the future. We know that features designed
for "local" use have a tendency to be deployed much more widely than
their designers intended.

   Brian

> In many of the cases we're discussing, the nodes inside an AD act "on
> behalf" of a source or sink, and that's the logic by which they are
> allowed such modification. HOWEVER, whenever you act on behalf of a
> source or sink, you ARE effectively a source or sink and thus beholden
> to the source/sink requirements, not merely router requirements.
> 
> I.e., if you want the performance of a router, act like a router and
> nothing more. If you want to act like a host, you need will have the
> performance of a host.
> 
> Joe
>