Re: [Softwires] New version of 4rd-U - with plain Encapsulation as a variant

Rémi Després <> Mon, 30 January 2012 09:22 UTC

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Date: Mon, 30 Jan 2012 10:22:19 +0100
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To: Maoke <>
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Subject: Re: [Softwires] New version of 4rd-U - with plain Encapsulation as a variant
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Hi Maoke,

Good to see you back in technical discussions, of which we had so many useful ones.
More in line.

Le 2012-01-29 à 05:38, Maoke a écrit :

> hi Remi,
> it a little confuses me that the new version introduces 2 variants

> - what is the technical difference of 4rd-U encapsulation variant vs. MAP-E? (except written in a single or some separated documents)

No difference (as said).

> on the other hand, it is unfair to state the benefit "Header-mapping provides more complete transparency to IPv4 packets than solutions using twice the IPv6/IPv4 translation of RFC6145" without mentioning the (at least the following two pieces of)

>  cost: 1.

Not clear AFAIK.
It can be discussed if you expand, but less subjective issues like those below are IMHO more important.

> losing the compatibility with single translation; 2.

I don't see this because, in my understanding:
- IPv6-only CPEs, in order to work with IPv4 shared addresses processed by BRs are stateless, MUST be modified anyway.
- Unmodified IPv6-only CPEs don't need to be modified to work with shared addresses processed by stateful NAT64/DNS64 (with known limitations NAT-related limitations, but this is understood). 
- 4rd-U can coexist with NAT64/DNS64 in ISP networks. (Provided IPv4 address-spaces used by NAT64 and 4rd-U are disjoint, there is AFAIK no operational issue.

If you have a specific configuration that illustrates your concern, it could be discussed with more details.

>  putting ICMPv4 PDU as the payload of IPv6 directly, with neither IP header nor ICMP header has the address checksum information - this will disable firewall preventing attacks.

For a site having a customer-provided CPE that integrates a firewall to take advantage of stateless IPv4-address sharing, its FW  MUST be upgraded anyway. Adding to it 4rd-U support is for this a logical solution.  
If the FW-CPE is not modified, its operation across IPv6-only networks remains IPv6-only (translatable to IPv4 by NAT64 if supported by the ISP).
Adding a note on this in the document would be possible, if found useful.  


> best regards,
> maoke
> 2012/1/29 Rémi Després <>
> Hello all,
> The new version of the proposed unified 4rd has just ben posted.
> It is available at:
> A major evolution since the previous version has been to have in it two variants.
> - The Header-mapping variant is as in the previous version
> - The Encapsulation variant is added after comments received, and accepted, that some use cases cannot be satisfied if the Header-mapping variant is the only one.
> Compared to the alternative approach of several MAP documents, the single-document approach is expected to avoid duplicate specifications, and to facilitate consistency checks of the design.
> Besides:
> - Header-mapping provides more complete transparency to IPv4 packets than solutions using twice the IPv6/IPv4 translation of RFC6145.
> - It has also the advantage of a simpler and self-sufficient specification.
> - The algorithm which permits BRs to forward datagram fragments without datagram reassembly is included.
> - The problem of fragmented datagrams from shared address CEs that must have different Identification if they go to common destinations is covered.
> - The design re-introduces the Domain IPv6 suffix which in some earlier 4rd designs, and somehow has been lost.
> - The port-set algorithm is without parameter.
> All questions and comments will be most welcome.
> Regards,
> RD
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