AW: AW: [En-Nut-Discussion] TCP problems

[Oliver Schulz]

Hi Harald and all,

Some minutes ago I commited my last changed/addition to the CVS.

I added a handler for incoming TCP options. Now requested MSS from peers are
stored and used in the TCP socket.

Cheers,
Oliver. 

> -----Ursprüngliche Nachricht-----
> Von: en-nut-discussion-bounces at egnite.de 
> [mailto:en-nut-discussion-bounces at egnite.de] Im Auftrag von 
> Harald Kipp
> Gesendet: Montag, 20. März 2006 09:53
> An: Ethernut User Chat (English)
> Betreff: Re: AW: [En-Nut-Discussion] TCP problems
> 
> Hi Oliver,
> 
> At 13:37 18.03.2006 +0100, you wrote:
> 
> >After several month of absence (or years? I can't remeber..)
> 
> Apart from some minor changes you main activity had been two 
> years ago.
> But it's great, that you constantly followed the development 
> and offered a helping hand from time to time.
> 
> 
> >It's not so hard to figure out what happened.
> 
> On my first look I can't see any problem at all. Possibly 
> because there is no FIN packet at second 0.84 in the capture 
> I received.
> 
> 
> >After reading the RFCs, this behaviour is OK, because the 
> FIN packet is 
> >justed queued into the data stream.
> 
> Agreed. SYN and FIN are part of the segments and count as 1 
> in the segment sequence number. Thus there is no need for any 
> delay before sending out a FIN. The segment with a FIN may 
> even contain data, if I remember correctly.
> 
> 
> >But (and now comes the error in Nut/OS), while exchanging the SYN 
> >packets, the peer requests a MSS (maximum segment size) of 
> 1260 bytes.
> 
> Definitely a major error. As a work around, Dusan should not 
> set the MSS to 1460. When traffic is routed via several 
> physically different networks, I'd strongly recommend to keep 
> the Nut/OS default anyway. Otherwise you risk packet 
> fragmentation, which Nut/OS generally can't handle.
> 
> See
> http://www.ethernut.de/en/medianut/
> 
> Btw. I still do not understand how this is handled. Some time 
> ago we were unable to connect to several public webservers 
> after our provider upgraded his software. Our local company 
> network is connected to the Internet this way
> 
>    Company Ethernet -> Router -> PPPoE -> DSL Modem
> 
> I had the idea, that max. sized Ethernet packets may not fit 
> in PPPoE frames. PPPoE has the same Ethernet packet size 
> limitation, but adds a header. So I reduced the MTU on my PC 
> and indeed all webservers were reachable then. After that I'm 
> unable to explain, why all other websites worked with the 
> original MTU.
> 
> In the meantime almost everything had been replaced or 
> upgraded and it is unknown, if any part had been buggy 
> previously. Everything is working fine today with max. MTU 
> settings and I have no idea, why.
> 
> Harald
> 
> 
> 
> 
> 
> 
> 
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