This is fine - it looks a like what I pointed to in the DCCP spec. But 
specifically,  I agree you don't need the DF flag visible - if you have a way 
to convey the info needed to set the flag at the transport (and anything else 
appropriate -as you note). I am all in favour of such appropriate abstraction.

Gorry

> On 12 Dec 2016, at 19:09, Joe Touch <[email protected]> wrote:
> 
>> On 12/12/2016 10:58 AM, Gorry Fairhurst wrote:
>>> 
>>> IMO, the app should never need to play with DF. It needs to know what it 
>>> thinks the transport can deliver - which might include transport         
>>> frag/reassembly and network frag/reassembly. 
>> How does the App handle probes for path MTU then in UDP? 
>> 
>> Gorry
> I think there needs to be two parts to the API:
> 
> - largest transmission size
> - native transmission desired (true/false)
> 
> If the app says "YES" to native transmission size, then that would suggest 
> that UDP would do *nothing* and pass that same kind of flag down to IP, where 
> IP would not only set DF=1, but also not source fragment.
> 
> I.e., I don't think it's the app's job to know how to explicitly control a 
> mechanism two layers down, and DF isn't really what you want anyway. DF isn't 
> the same as "don't source fragment".
> 
> Joe
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