?
Solved

16,580 byte packet

Posted on 2004-10-01
5
Medium Priority
?
351 Views
Last Modified: 2013-12-07
Been watching traffic (file transfers between windows machines.)   I noticed this:
http:/mvpbaseball.cc/capture.jpg

Can 16,580 bytes really be sent in one packet?  I thought the MTU of ethernet was 1500
0
Comment
Question by:dissolved
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
5 Comments
 

Author Comment

by:dissolved
ID: 12209407
anyone?
0
 
LVL 2

Expert Comment

by:VertigoRay
ID: 12214687
As for 1500 being the max packet size, I believe that Win2k (pre SP1) defaulted UDP at 2000.  Of course after some SP releases they changed it to 1465.  This was done to make sure Kerberos didn't have any issues, since that's the basis of 2k3's authentication/encryption/etc.  So basically, the max packet size is dependant on the protocol.

SMB packet sizes can get much larger than the typical TCP/IP packet size.  The global option of "max xmit" sets the maximum size of packets that Samba exchanges with a client.  In some cases, setting a smaller maximum packet size can increase performance, especially with Windows for Workgroups.  The default value for this option is 65535. You can override it as follows:

[global]
      max xmit = 4096

Since the percentage of each block required for overhead falls as the blocks get larger, max xmit is conventionally set as large as possible.  It defaults to the protocol's upper limit, which is 64 kilobytes.  The smallest value that doesn't cause significant slowdowns is 2048.  If it is set low enough, it will limit the largest packet size that Samba will be able to negotiate.  This can be used to simulate a small MTU if you need to test an unreliable network connection.  However, such a test should not be used in production for reducing the effective MTU.  Normally, one tries to set these socket options high.  The value of 16384 has been suggested as a good starting point: in a non-Samba test.  This starting point seems pretty close to your packet size.  Is this coincidence?
0
 

Author Comment

by:dissolved
ID: 12216290
Are you speaking about MSS or MTU?  I"m confused. Say I  have an MSS of 1460 (which I do in thise case) and the MTU of ethernet is 1500bytes as we all know. ...So how is a 16,580 packet being sent?  First off, it *should* be sent as several segments instead of one.  Also:   Surely there are intermediate routers that are there whose interface has an MTU of 1500. If I send a 16580 packet via SMB protocol (which utilizes TCP), it's going to get fragmented.

However in my case this the packet never leaves my immediate network and the receiver receives the packet and indicated it wa indeed 16,580 bytes..  Any clarification appreciated.
0
 
LVL 2

Accepted Solution

by:
VertigoRay earned 2000 total points
ID: 12234063
I found the s ite where I read a lot of what I learned about this.  Here's a link for a topic that is closest to what you're asking (save me some key strocks if I just paste you the link):

http://www.aarnet.edu.au/engineering/networkdesign/mtu/size.html

I hope this helps!
0
 

Author Comment

by:dissolved
ID: 12242810
great read thanks
0

Featured Post

Create the perfect environment for any meeting

You might have a modern environment with all sorts of high-tech equipment, but what makes it worthwhile is how you seamlessly bring together the presentation with audio, video and lighting. The ATEN Control System provides integrated control and system automation.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

WARNING:   If you follow the instructions here, you will wipe out your VTP and VLAN configurations.  Make sure you have backed up your switch!!! I recently had some issues with a few low-end Cisco routers (RV325) and I opened a case with Cisco TA…
This article explains the fundamentals of industrial networking which ultimately is the backbone network which is providing communications for process devices like robots and other not so interesting stuff.
Internet Business Fax to Email Made Easy - With  eFax Corporate (http://www.enterprise.efax.com), you'll receive a dedicated online fax number, which is used the same way as a typical analog fax number. You'll receive secure faxes in your email, f…
Michael from AdRem Software outlines event notifications and Automatic Corrective Actions in network monitoring. Automatic Corrective Actions are scripts, which can automatically run upon discovery of a certain undesirable condition in your network.…
Suggested Courses

752 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question