Re: [Softwires] Unified proposal for stateless IPv4 Residual Deployments (4rd-U) - Contributors?

Ole Troan <> Tue, 29 November 2011 18:47 UTC

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Subject: Re: [Softwires] Unified proposal for stateless IPv4 Residual Deployments (4rd-U) - Contributors?
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to summarize my view:
 - the 4rd-u proposal (including the changes you plan) are well understood
 - the main ideas from 4rd-* are already incorporated into MAP
 - 4rd-u is a slightly different way of doing translation (calling mapping doesn't change that fact)
   go to behave to argue if yours is better than what was specified there.
 - I think it is the wrong thing for this working group to encourage development of yet another solution, when we already
   have many.
 - I would also like to see one solution, my choice is encapsulation. given that all the building blocks already exist, I
   would expect we'll see translation in the wild too, whatever we choose to do in the IETF. ref: NAT464.

I really hope this is the last I'll ever write on this topic.


On Nov 29, 2011, at 19:11 , Rémi Després wrote:

> Le 29 nov. 2011 à 17:15, Ole Troan a écrit :
>> Remi,
>>> For those who attended the Softwire session in Taipei, please note that the serious objection against 4rd-U expressed by several participants during the meeting has been, soon after, acknowledged to be invalid (
>>> Also, other (less important) objections have been answered in, without reaction so far. 
>> I do not think that's a fair representation.
> It was intended to be one, and is still believed to be so (see below)
>> the main objection to 4rd-u is that it is 'just another translation' solution.
> a)
> That's not what I heard during the meeting.
> Both Mark Townsley and Dave Thaler, taking for granted your statement that checksum-neutral addresses of 4rd-U would cause "address spray", said firmly that 4rd-U should be rejected because it wouldn't work.
> In my understanding, not working is a show stopper, which I call a "main objection".
> b) If your main objection is that 4rd-U would be 'just another translation', it is ALSO invalid. 
> If you have read my answer to your list of objections, you should know that 4rd-U is a reversible-header-mapping solution, and as such is based on neither translation nor encapsulation. (actually a tunnel closer to encapsulation in my understanding).
>> how many do we need?
> Many consider that, if there is the choice, ONE standard is better than several.
> The point is that 4rd-U combines advantages of double translation and encapsulation with only a slightly different tradeoff between optimizations of header-length and processing time.
> Doubts are legitimate as long as the specification is incomplete, but that's why more work is needed.
>> it doesn't appear to offer any benefits compared to the already specified solution.
> Which solution? (So far, there are two in the pipe - translation and encapsulation.)
> Meeting requirements of both solutions is AFAIK a benefit.
>> as it stands it will just result in 3 ways of doing the same thing, instead of 2.
> Different view on this.
> Three standards would make no sense.
>> the topic discussed in softwires, wasn't the main objection. as far as I can see, "checksum neutrality" does not offer any advantages over incrementally updating the L4 checksum.
> Again, commenting my previous answer to your list of objections would be be more constructive than repeating that 4rd-U doesn't do anything without arguing on substance.
> Since there is no obligation to comment, please refrain from criticizing a solution without commenting previous answers made for you.
>> every node doing this will have to look into the L4 header anyway.
> Sure. IPv4 address sharing implies _looking_ at port fields (true also for encapsulation).
> But this doesn't imply that L4 data need to be  modified, especially if these modifications need to depend on whether the protocol is TCP UDP, DCCP, etc. 
> Encapsulation and reversible header mapping don't care about this, which is one of their virtues.
> Cheers,
> RD