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)
> 
> 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
> 
> 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.
> 
> 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


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