Hi Gert,
Many thanks for your kindly explanation, I think I have missed the stream
and connection oriented characteristic of TCP, which you have figured out.
So my problem might be caused by some device in my network which has lower
MTU and cannot send ICMP message to one of client/server to adjust the
outer TCP mss correctly.
Since I have stated before, I have no control of the network, so I have
changed to mssfix and solved the issue, maybe this will have little impact
on the throughput however that's not the main concern currently.
And back to my original question, should we can say in *rare* cases, the
mssfix can also be applied to TCP connection mode?
Sorry for not CC to openvpn-users maillist for others information.
2016-02-29 18:26 GMT+08:00 张东亚 <fortitude.zh...@gmail.com>:
> Hi Gert,
>
> Many thanks for your kindly explanation, I think I have missed the stream
> and connection oriented characteristic of TCP, which you have figured out.
>
> So my problem might be caused by some device in my network which has lower
> MTU and cannot send ICMP message to one of client/server to adjust the
> outer TCP mss correctly.
>
> Since I have stated before, I have no control of the network, so I have
> changed to mssfix and solved the issue, maybe this will have little impact
> on the throughput however that's not the main concern currently.
>
> And back to my original question, should we can say in *rare* cases, the
> mssfix can also be applied to TCP connection mode?
>
>
>
> 2016-02-29 16:01 GMT+08:00 Gert Doering <g...@greenie.muc.de>:
>
>> Hi,
>>
>> On Mon, Feb 29, 2016 at 11:32:13AM +0800, ????????? wrote:
>> > Thanks for your kindly explanation, since the outside network is
>> provided
>> > by an IDC, I cannot investigate much.
>> > I think you means the path mtu discovery by referring to the ICMP
>> > unreachable, this does help to adjust the *outside* TCP mss, however,
>> how
>> > openvpn can affect the *inner* TCP mss after the outer mss have been
>> > adjusted? Do I need to turn on some options? or openvpn do internal
>> > fragmentation for the inner TCP packets?
>>
>> This is TCP, so the size of the inner packets is irrelevant - if it's too
>> large, it will get split over two outer TCP packets (by the TCP layer).
>>
>> OpenVPN just stuffs a big chunk of data down the TCP socket, just as a
>> web server would - and it's TCP's job to ensure that the resulting packets
>> are not too large for the network they are traversing.
>>
>> This is very different when using UDP: since UDP has no concept of
>> "segment size" and "path MTU", you'd get IP-level fragmentation if the
>> packets you stuff into the UDP socket is too big - and there are too
>> many networks and borken NAT routers that cannot deal with fragments,
>> so --mssfix helps avoiding this for the UDP case.
>>
>> gert
>> --
>> USENET is *not* the non-clickable part of WWW!
>> //
>> www.muc.de/~gert/
>> Gert Doering - Munich, Germany
>> g...@greenie.muc.de
>> fax: +49-89-35655025
>> g...@net.informatik.tu-muenchen.de
>>
>
>
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