Large MTU

Hello

If I use MTU = 9000 (on both sender and receiver), sometimes iam
getting very low performance of 4 to 5MB/sec on a gigabit network (2
machines crossover cabled). But sometimes i get 110 MB/sec.

When i get the low performance, if i change the MTU (on receiver) to
something <= 8000 Iam getting the proper performance.

If I rollback to 9000, iam facing the problem again. It persists
until I reboot the box.

Env
===
Receiver
=========
Linux 2.4.19 SMP
Intel e1000 4.4.19

Sender
======
Linux 2.4.19
Intel e1000 4.4.19

thanks

ssk wrote:

> Hello
>
> If I use MTU = 9000 (on both sender and receiver), sometimes iam
> getting very low performance of 4 to 5MB/sec on a gigabit network (2
> machines crossover cabled). But sometimes i get 110 MB/sec.
>
> When i get the low performance, if i change the MTU (on receiver) to
> something <= 8000 Iam getting the proper performance.
>
> If I rollback to 9000, iam facing the problem again. It persists
> until I reboot the box.

Ethernet doesn't support MTU larger than 1500 bytes.


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James Knott <(E-Mail Removed)> wrote:
> ssk wrote:
>> If I use MTU = 9000 (on both sender and receiver), sometimes iam
>> getting very low performance of 4 to 5MB/sec on a gigabit network (2
>> machines crossover cabled). But sometimes i get 110 MB/sec.
> Ethernet doesn't support MTU larger than 1500 bytes.

But certain Gigabit Ethernet NICs and switches support a non-standard
JumboFrames spec that allows an MTU of 9000 bytes.

What is being used to measure the performance? What send sizes is it
using? Does netstat report packet losses?

rick jones
--
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