Re: [manet] On Forwarding-and-regeneration (was: Re: draft-ietf-manet-aodvv2-13 review

Just be careful to note that this concept is as currently being discussed (a) specific to AODVv2, and (b) not an application of 7182, which has no knowledge of special TLVs.

This is something we'd want to get right, and need to get right if in any space not specific to ADODVv2, because getting it wrong produces future problems.

I can see some possible approaches, none is ideal and we're rather out of time to specify. But this is experimental, so I think we might be able to indicate the shape of the solution without specifying it, which would be a different RFC, under a bit less time pressure. (Extensions to existing protocols like 7182 would naturally be in scope rechartered I think.)

To indicate the range that's open, here are two possible ideas, one of which has an impact now, so needs to be agreed. Note that I'm not suggesting (in fact quite the opposite) defining an extension to 7182 here, rather enabling such an extension, if written, to "do the right thing".
- We have an extension to 7182 that says "zero out all value octets in protocol specific TLVs. That requires now putting the AODVv2 metric TLV in that space.
- We have an extension to 7182 that adds extra material to the value field that indicates (TBD how, by position with sanity check that this is TLV value perhaps?) which octets are to be zeroed out before the ICV is calculated.

We do not have the time to specify this in an acceptable manner within two weeks though. But the security consideration section could say something along the lines of "this enables the use of an ICV defined to zero out these octets".

-- 
Christopher Dearlove
Senior Principal Engineer
BAE Systems Applied Intelligence Laboratories
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-----Original Message-----
From: manet [mailto:manet-bounces@ietf.org] On Behalf Of Lotte Steenbrink
Sent: 22 April 2016 10:28
To: Henning Rogge
Cc: Mobile Ad Hoc Networks mailing list
Subject: Re: [manet] On Forwarding-and-regeneration (was: Re: draft-ietf-manet-aodvv2-13 review - a couple of big ticket Items)

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Hi Henning,

> Am 22.04.2016 um 11:08 schrieb Henning Rogge <hrogge@gmail.com>:
> 
> On Fri, Apr 22, 2016 at 11:05 AM, Lotte Steenbrink 
> <lotte.steenbrink@fu-berlin.de> wrote:
>> Hi Thomas,
>> Can it?! Iirc, the reason why we adopted the “regeneration” language 
>> in the first place is that we’ve been told that whenever one bit in 
>> the message (apart from its header) is changed, the entire thing has to be regenerated.
>> I’m starting to get the feeling we’ve just been misunderstanding each 
>> other for more than a year. :( Anyway, it seems like we’re getting 
>> close now, so yay.
> 
> "Modifying" the binary message instead of parsing and generating a new 
> one will be difficult as soon someone writes an extension to AODVv2 
> that adds more TLVs to the message.
> 

D’oh, right. Yeah, if I remember it correctly, that’s what you explained to me when I got confused about the topic last spring… But– even if a message contains TLVs that the AODVv2 implementation handling it doesn’t understand, it will still be able to recognize the Metric TLV, right? Isn’t that the nifty thing about RFC5444? So, while we really shouldn’t write “before calculating the ICV, set the n-th 4 octets to 0”, we might say “identify the octets that make up the metric value and set those to 0”?

Best regards,
Lotte

> Henning Rogge

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