hi Yiu, sorry but i just found i missed a technical issue you left in this message.
2012/4/9 Lee, Yiu <[email protected]> > > on the other hand, 4rd-u makes a tight coupling between the address > format > and its own header mapping mechanism. this makes an operator unable to > have > different choices of transition mechanism as long as it chooses 4rd-u. > if > you concern the choice of IPv6 transition mechanism, i do recommend > MAP, as > either encapsulation or translation is operatable with MAP address/port > mapping without difficulty. > > [YL] Sorry for my lack of knowledge. Please explain how MAP isn't coupling > address format and header mapping? > tight coupling here, i mean, that 4rd-u header mapping mechanism sometimes depends on features of the address format, like the CNP and the V-octet. for example, it removes the L4 checksum adjustment, this makes the whole system MUST following the addressing with CNP. for the MAP, things are different. boxes are implemented with existing header processing modules but only need to add MAP address mapping module into them. once the operator deploys MAP following its addressing plan paradigm (we are still working on a better guidance for this in the MAP deployment draft), the operator can choose either MAP-T or MAP-E for the header mapping without the need of changing their addressing plan. if the operator find translation is suitable for this part after a certain period of practice on encapsulation, it can switch the mode by informing the CE to change the mode of working (surely sometimes such an action of informing is not easy in practice for, e.g., the home CE subscribers but it is feasible for enterprise networking). another example of de-coupling is translation approach: RFC6052 defines a stateless address mapping while RFC6145 defines the header processing which is usable for both stateless and stateful solutions, both 1:1 case for non-renumbering transition and residual deployment of MAP. implementation does also benefit from the de-coupling. the RFC6145 translation module can directly work with address mapping module of MAP or RFC6052. the MAP address module can work with header processing module of RFC2473 (for MAP-E) or translation module of RFC6145 (for MAP-T). it doesn't mean the tight coupling doesn't work. like the Burton snowboard, it works fantastically with its own system of bindings, not interchangable for other brands ;-) however, in most of time, we really think interchangability, supported by loose coupling, is preferred. cheers, maoke
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