This is a good point. When I get some time I'll dig out the MS stuff and =
RFC and check out NetBSD's behaviour. This will take a few days as I'm =
quite busy right now. If anyone else can't wait then drop me a line and =
I'll tell you where I found what I said in my last mail

A.

--
Alex Barclay			E-mail: alex@vsys.com
Vsys				Tel:	+1 719 635 8066 x 17
731 N.Weber, Suite 202		Page:	+1 719 477 5190
Colorado Springs, CO 80903	Fax:	+1 719 635 1420


-----Original Message-----
From:	Jukka Marin [SMTP:jmarin@pyy.jmp.fi]
Sent:	Monday, September 22, 1997 10:27 PM
To:	Alex Barclay
Cc:	'Ignatios Souvatzis'; tech-kern@NetBSD.ORG
Subject:	Re: TCP Problems (Was: RE: Windows packet size?)

On Mon, Sep 22, 1997 at 10:38:29AM -0600, Alex Barclay wrote:

> 1) Micro$haft are following one of the RFC's for enhancing TCP =
throughput
> by avoiding fragmentation (hence the DF flag that you see)
>=20
> 2) When a MS box tries to establish a connection it sends its MSS. The =
dest
> box replies with its MSS and MS takes the lower. (As an example - the =
box
> I'm running on here sends an initial MSS of 16K - I'm on token ring, =
my
> NetBSD box (about 20 hops away) replies with an MSS of 1496 (or
> thereabouts), MS now uses an MSS of 1496 and sets DF
>=20
> 3) Assume we have a ppp link in the way which is using an MTU/MRU of =
256
> (which il legal providing that it will correctly receive a 1500 byte =
packet)
> then the gateway that has the PPP link should send an ICMP host =
unreachable.
> This ICMP will trigger MS to reduce their MSS.
>=20
> 4) A problem is that quite a few routers will dump the packet but fail =
to
> send the ICMP meaning that the link locks up and eventually fails. MS =
do
> present a strategy that should overcome this.

Then NetBSD must have this problem.  I use NetBSD 1.2 machines as =
routers
and my win95 system can't talk to the net properly because my PPP link =
has
MTU of 576 bytes (or so, much less than 1500 bytes anyway).  If I change
MTU to 1500, everything works ok.

  -jm


--=20

                       1503 kHz @ 21:30 EET DST Mon-Fri

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