Thoughts on increasing MTUs on the internet

Sat Apr 14 17:22:16 UTC 2007

On Apr 13, 2007, at 4:55 PM, Fred Baker wrote:

> The biggest value in real practice is IMHO that the end systems  
> deal with a lower interrupt rate when moving the same amount of  
> data. That said, some who are asking about larger MTUs are asking  
> for values so large that CRC schemes lose their value in error  
> detection, and they find themselves looking at higher layer FEC  
> technologies to make up for the issue. Given that there is an  
> equipment cost related to larger MTUs, I believe that there is such  
> a thing as an MTU that is impractical.
>
> 1500 byte MTUs in fact work. I'm all for 9K MTUs, and would  
> recommend them. I don't see the point of 65K MTUs.

Keep in mind that a 9KB MTU still reduces the Ethernet CRC  
effectiveness by a fair amount.  Adoption of CRC32c by SCTP and iSCSI  
has a larger Hamming distance restoring the detection rates for Jumbo  
packets.

-Doug