LAN vs. WAN MTU setting

BallsOutPunk · Post by **BallsOutPunk** » Thu Jul 03, 2003 5:09 am

I have a question about optimizing my connection through a router, which is something I'm still a little new to. Ok, when I go to the IP of my router and go through the configuration settings, it has a setting for the WAN MTU. Of course, I want this to be 1500. Here's the part I don't understand... Should my computer's MTU also be set to 1500 or should it be something else to work better with the LAN? Am I setting myself up for fragmentation on my LAN with a 1500 MTU on my computer? I recently ran the SG TCP Optimizer and did the "find the largest possible non-fragmented packet" test, and it said to set my MTU to 1300, and the largest unfragmented packet was 1272 bytes.

Before, when my computer was directly connected to the cable modem, I manually sent pings at the dos/command prompt and packets of the usual 1472 went through unfragmented. This makes me think I don't have it set up right.

Thanks in advance for responses!

Adam

blin2000 · Post by **blin2000** » Thu Jul 03, 2003 11:37 am

Accounding to MS, Windows defaults to 1500 but that size is often incompatible with PPPoE. You may set The default and maximum PPPoE MTU size upto 1,480 bytes. For more tips or information, go to http://www25.brinkster.com/ChicagoTech

Robert, MS-MVP/MCSE and CNE
Windows & Network Support, Tips and FAQs on
http://www25.brinkster.com/ChicagoTech

BallsOutPunk · Post by **BallsOutPunk** » Mon Jul 07, 2003 1:50 am

blin2000 -

I don't really understand why PPPoE would play into this at all. Not to say it doesn't, I just don't see why. Does 802.11b rely on PPP? The only protocol enabled by the network connection on my computer is TCP/IP. I also could not locate any relevant info on your site; that is when searching for PPP, PPPoE, wireless, 802.11, MTU, etc.

blin & everyone else -

To be more specific about my original question... I know that I want the MTU to be 1500 over the WAN (i.e., my cable connection). There is an option within the configuration pages of for the router to set the MTU over the WAN, which I do have set to 1500. What I'm asking is: Should the settings on my computer be something else to optimize the connection over my WLAN?

Murman · Post by **Murman** » Mon Jul 07, 2003 5:48 am

no 1500 is good for the internal LAN as well, i.e. your reg settings.

As long as you have good wireing your all set..

BallsOutPunk · Post by **BallsOutPunk** » Fri Jul 11, 2003 3:37 am

Originally posted by Murman
no 1500 is good for the internal LAN as well, i.e. your reg settings.

As long as you have good wireing your all set..

murman -

It's wireless, but I don't think that's going to matter in this case. If 1500 works across a wired LAN, it seems that it should work just as well across wireless. My only real question is would it result in fragmentation. Apparently, it doesn't. Thanks for the reply.

PS - I've got experience working with wired LANs, I just wanted to make absolutely sure that the same settings would be fine with wireless in this case.

Post by **Philip** » Sun Jul 13, 2003 10:05 am

1500 for MTU works best with broadband, LANs and WLANs the same... You get to transmit more data with less overhead (headers), and it is optimal to have the same size MTU across the entire connection to avoid fragmentation.

I also have an article on MTU size on the main site, if you're interested: http://www.speedguide.net/read_articles.php?id=111