Re: [v6ops] PMTUD issue discussion

[joel jaeggli <[e-mail]>]

I think this is worthwhile and I will work to incorporate the observation.

On 8/26/14 2:50 AM, Andrew 👽  Yourtchenko wrote:
> Joel,
> 
> On 8/25/14, joel jaeggli <[e-mail]> wrote:
>> On 8/25/14 1:49 PM, Joe Touch wrote:
>>> Hi, all,
>>>
>>> Speaking from TCPM-land, I would observe the following:
>>>
>>> - PMTUD already has many known problems, which is why PLMTUD is
>>> recommended instead
>>
>> I agree, operationally however I'm trying not to break existing devices
>> attempting to connect to me, is the motivation for the note.
>>
> 
> During the presentation in the v6ops session I made a comment about
> sysctl net.ipv4.tcp_mtu_probing. Since then I had a chance to test it
> - and indeed, it affects the behavior of TCP over IPv6 as well.
> 
> However, the value of 1 causes a large value of MSS to be used,
> resulting in about 1.5 second hiccup. So, yeah it "works" but for
> barely acceptable values of "works"
> 
> Setting the value to 2 causes the initial MSS to be 512, which
> "mitigates" the problem and avoided the hiccups on a 100kb file I was
> testing with - at the expense of almost 3x more packets of course.
> 
> I think it would be useful to see the discussion of this measure and
> its applicability/tradeoffs in the draft.
> 
> --a
>