RE: calculate correct MTU size for jumbo frames?

From: Matthew Zito <>
Date: Sun, 9 Nov 2008 00:21:50 -0500
Message-ID: <>

9000 is the most commonly used value, and as a nice round value, less opportunity for misconfiguration. Some old switches could only do 4400 bytes, but at this point, you should just set it at 9k with the rest of the world ;)

If you did want to calculate, you just need to sort out ethernet overhead + ip overhead + tcp overhead, which based on this site (first hit on ethernet overhead on google) is 44 bytes.


-----Original Message-----

From: on behalf of Martin Berger Sent: Sat 11/8/2008 4:36 PM
Subject: calculate correct MTU size for jumbo frames?  

Hi out there,

I'm searching for a formula how to calculate a MTU size for the private interconnect of an ORACLE RAC.
I found some documents which suggest to increase MTU size to 9k. Unfortunately my Network admins asked me to specify the MTU size a little bit better (they called it 'some bytes less than 9k') as they fear some known issues on existing infrastructure with exactly or 'too closed to' 9k.
I'm sure there must be a way to calculate the max blocksize of the messages for a Cache fusion communication woth a DB having 8k blocksize. Or is the whole communication that flexible so there is never a dedicated max.blocksize? In this case I would welcome some more informations about cluster private communication ;-)

thank you for any help, suggestion, URL, ... ;-)



Martin Berger

-- Received on Sat Nov 08 2008 - 23:21:50 CST

Original text of this message