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

Joe Touch <touch@isi.edu> Wed, 27 May 2015 20:32 UTC

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Date: Wed, 27 May 2015 13:31:58 -0700
From: Joe Touch <touch@isi.edu>
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To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Gert Doering <gert@space.net>
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Subject: Re: [v6ops] Extension Headers / Impact on Security Devices
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On 5/27/2015 1:29 PM, Brian E Carpenter wrote:
> 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.

See the rest of my response below, then.

Joe

>    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
>>