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

[rishi]

Is there a way to  turn off TCP checksumming in linux or windows? It's
easy to turn off in lwIP, but the linux/windows client then drops the
packets with bad checksums.

Rishi

> 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
>
>
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