Re: [Softwires] IPv4 Residual Deployment - Unified-standard proposal 4rd

[Rémi Després <[e-mail]>]

Le 2012-03-14 à 10:00, Maoke a écrit :

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> 2012/3/14 Rémi Després <[e-mail]>
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> Le 2012-03-14 à 06:51, Maoke a écrit :
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>> 2012/3/13 Rémi Després <[e-mail]>
>> 2012-03-13 12:02, Maoke :
>>> 2012/3/13 Rémi Després <[e-mail]>
>> ...
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>>>> The 4rd mechanism is for protocols that have ports at their usual place (all existing protocols that have ports have them at the same place, even if using another checksum algorithm like SCTP).
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>>> may you have a check on the statement of "all existing protocols" again? i noticed RFC908/RFC1151. sorry if that are not a transport protocol over IP. 
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>> I missed this one.
>> None of the proposed stateless solutions supports it, but it remains that you are right: it has ports at a different place.
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>> alright. so 4rd-U doesn't not support "all existing transport protocol" either.
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> Never said that without qualifying which protocols.
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>> but i suppose you may make an update in the 4rd-u-06 so that a new "if...else..." is added the port pick-up logic, and surely the CNP is not a problem for RDP because the old version (RFC908) has 32bit checksum but not involving pseudo-header while the newer version (RFC1151) changed to use TCP-checksum. no big deal but only needs a new patch to the draft.
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> In the Note in 4.4 (7), the first sentence is:
> "This guarantees that, for all protocols that use the same checksum algorithm as TCP, Tunnel packets are valid IPv6 packets, and this independently from where the checksum field is placed for each protocol."
> It can become: 
> "This guarantees that, for all protocols that use the same checksum algorithm as TCP and have ports at the same place, Tunnel packets are valid IPv6 packets, and this independently from where the checksum field is placed for each protocol."
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> Similarly, in the comparison table, H6 is:
> "For shared IPv4 addresses, DCCP and UDP-Lite supported, as well as future  protocols using the TCP checksum algorithm"
> It can become:
> "For shared IPv4 addresses, DCCP and UDP-Lite supported, as well any future protocol that might use the TCP checksum algorithm and ports at the same place"    
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> then it is fine. with these statement, 4rd-U can support 
> - TCP 
> - UDP
> - DCCP
> - any future or less well-known protocol as long as it uses TCP checksum and port at the same place
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> as a counterpart, we may suggest MAP-T to state it supports 
> - TCP
> - UDP
> - DCCP (with enforcing it rather than RFC6145's "optional") 
> - any future or less well-known protocol, no matter what layout it is nor how the checksum is defined, with the similar logic of L4 checksum recalculation 

Maybe I get the point you are making: you implicitly consider that BR and CE modifications can be synchronized. This is feasible if ISPs provide all CE nodes, but not in the general case.
  
Changing DCCP support from optional to mandatory in RFC6145 isn't backward compatible (an upgraded node isn't guaranteed to interwork with a non upgraded node).
 
To be even more precise, H6 of the comparison table can be:
"For ISPs that don't provide all CE nodes, and for shared IPv4 addresses, DCCP and UDP-Lite are supported, as well as future protocols using the TCP checksum algorithm and ports at the same place"

Does this cover the point?

RD




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> ;-)
> maoke 
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>> but this is not my point. my point is: there must be something we don't know ("non omnia possumus omnes"). even we have gone through the RFCs, there might be some other proprietary L4 protocols, or experimental protocols. even they are minority, i don't think ignoring their existance in our solution fits the spirit of the Internet. it might be argued that NAT44 doesn't support such L4 protocols now, but an L4 protocol owner may makes his own NAT44, either attached to the CE or separated. if 4rd-U respects such an effort, it should state "currently blahblabla L4 protocols are supported". the similar statement applies to the RFC6145 or MAP as well.
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>> i somehow am hard to accept words like "far fetched theoretical problem". 
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> If I had thought it might be so, I would have avoided the word.
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>> the L4-recalculate is a generic, architectural solution, surely needing codes for every L4 protocol. but this generality in architecture makes RFC6145 or MAP-T equipment be easily enhanced to support anything new with the same logic. but for the 4rd-U BR, it looks to me we cannot have the unified logic for all (even limited to existing and well-known) L4 protocols. 
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>> only my 2 cents. 
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> With amendments above, the point is AFAIK completely covered: everything is rigorously true, and worth noting.
> Thanks for the useful reference to the RDP of RFC1151.
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> RD 
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