Re: AD comments on draft-ietf-rohc-hcoipsec-10

Carsten Bormann skrev:
> Magnus,
> 
> thank you for the quite thorough review of the ROHCoIPsec documents.
> 
> Let me focus on this one comment right now as it is quite dear to my heart.
> I definitely agree that the MTU variability caused by header compression
> merits discussion.
> (I'm just now running into a different manifestation of it in 6lowpan.)
> 
> I'm just not sure the discussion should be done as part of ROHCoIPsec.
> There are other applications of header compression in tunnels, e.g.
> 4901, 4170.
> As I mentioned, adaptation layers also might run into problems here; I'm
> not even sure basic ROHC (3095/5225) is immune to this problem if there
> are relevant MTU restrictions coming from L2 (normally, PPP has a larger
> MTU than Ethernet and so we just don't notice).
> 
> I'd prefer to have this discussion in a more general form.
> This would probably involve (PL)PMTUD experts and HC experts, both from
> ROHC and maybe from INT WGs such as 6lowpan.
> Clearly, there is enough related work about tunnels in TSVWG right now.
> 
> I would change my mind if there was something specific that ROHCoIPsec
> can do that does not apply to the other versions of this issue, but
> right now I'm lacking imagination what that could be.
> 

Carsten,

I agree that this is a generic issue that do occur for both header
compression and any tunnel technology that has a variable overhead.
However, ROHCoIPsec do have a few special issues that brings these
issues to the forefront.

- Turns of the usage of ROHC segmentation that could be used for dealing
with this issue. However, I think turning off segmentation is the right
choice but forces us to deal with the resulting PMTUD problem.

- That we have noticed it in this case. I don't find it acceptable to
punt on the issues just because it should have been dealt with earlier.

So yes general discussion is good as it is a generic issue. However,
this document set needs to both document it and have some consideration
on what to do with it.

I will try to start a discussion on this across some WG and area lists
and hold the discussion on TSV-area.

Cheers

Magnus Westerlund

IETF Transport Area Director & TSVWG Chair
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