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Re: [MiNT] Mintnet success ?

Peter Slegg wrote:

On Wed, 14 Nov 2007 16:30:26 -0500, Mark Duckworth <mduckworth@atari-source.com> wrote:

The MTU of ethernet is 1500.  Under will definitely work fine, but you
will incur more overhead.  Sounds to me like you're ahead of the game
though seeing as how it's actually working.  I don't think this is
negotiable when it comes to setting it higher though :-P  The fact that
it's working indicates an undersized/corrupted buffer somewhere (or
perhaps a defect with the card).

Thanks,
Mark



I've tried several different drivers and 3 different cards so we
can eliminate those possibilities.

Why does lo0 have mtu bigger than 1500 ?

lo0:    flags=0x4b<UP,BROADCAST,LOOPBACK,RUNNING>
        inet 127.0.0.1 netmask 255.255.255.0 broadcast 127.0.0.255
        metric 0 mtu 16384

Is 1500 a Mint limitation ? On a linux box I could ping packets
much bigger than 1500

Peter
You're thinking of different things. An ethernet frame is 1500 bytes. ping is ICMP protocol which is higher level than the ethernet packet and can do things like send several 1500 byte packets in order to make up whatever sized ICMP packet you are sending. In fact even though ethernet has a 1500 byte packet size, you can actually send less due to overhead. BUT if you tell your system your underlying device can handle larger packet sizes and the buffers/protocol cannot the end of every packet would be truncated. 

So you have a packet [---]
You have a large chunk of data (which is many packets) [---][---][---][---][---] And if you set your MTU too high the end of the packets will get cut off giving you packets with the ends cut off so you get [---[---[---[---[--- If you can understand what I am saying.
In your case, there's probably some pause between each packet send. The lower MTU probably adds enough overhead and slows things down just enough that the corruption disappears. I've seen things like this with serial on my older machines.
You've tried different cards but did you try different ISA slots (milan) or ethernecs? I'm willing to bet it would be hard to eliminate all of the possibilities (swap machine with same boot disk) due to lack of hardware. 

Thanks,
Mark