Re: [lwip-users] Try to Increase Jumbo Packet size beyond 9K

[Timmy Brolin]

address@hidden wrote:
> Kieran Mansley wrote:
>> On Mon, 2008-10-13 at 08:58 -0400, bill wrote:  
>>> TCP checksum (which we in the end disabled because we are always on an
>>> internal lan)     
>> I hope you're not transferring any important data over this connection.
>> I would not trust any network to get the bits right all the time.  It
>> would be fine for a large class of applications (e.g. where the data has
>> no persistence when it arrives, or for those that would often use UDP)
>> but a really bad idea for others.
>>   
> I agree on this. We only discovered a bug in one MAC because of TCP
> checksum errors. The MAC said the CRC was correct...
>
> Simon
Why? The Ethernet 32bit CRC is lightyears better than the 16 bit TCP
checksum at detecting errors (unless your MAC is broken of course...)
Modern industrial Ethernet protocols for example cannot afford a lot of
overhead per packet, so they rely entirely on the Ethernet CRC.

Which reminds me... I read somewhere that the effectiveness of the
Ethernet CRC drops somewhat at a magic packet size somewhere around 9k.
So if data integrity is important, you should not use 16k jumbo frames.

4k jumbo frames may be useful in some systems if it means you can use
the MMU to move the payload around rather than having to copy it.

/Timmy Brolin