[e2e] Layering vs. modularization

Joe Touch touch at ISI.EDU
Thu May 15 19:35:44 PDT 2008


David P. Reed wrote:
> The following argument that you make by dragging in "fate sharing" 
> suggests that your mental model is not about layering at all.  You are 
> discussing dynamic behaviors, and layering has NOTHING to do with 
> dynamics of packet transport, and more than modularity in a programming 
> language has anything to do with the speed of a CPU's various ALU and 
> memory operations.

I gave a specific example below of cases where it's useful for one layer 
to expose information (in this cases, groups of V4 addresses within a 
single V6 address) to another. That's precisely about layering, and 
something that elsewhere has been called layer violation.


>>> stateful packet inspectors *might* need a re-write, but that aside, I 
>>> don't see  how anything other than a bug would make the outer V6 
>>> active units need to read the inner V4 payload, or vice versa
>> Outer V6 would read inner V4 to support path 'fate sharing', i.e., 
>> when doing multipath routing it's useful to ensure that 'flows' 
>> traverse similar paths, and in this case the V4 address could be the 
>> best cue to a flow.
>> Joe

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