Which will be best MTU

Posted on 2009-05-12
Last Modified: 2012-08-14
Which will be best MTU size for our company systems?

By which internet browsing/downloading will be faster.

We have
- Peer 2 Peer environment
- Desktops / Laptops
- 22 Systems
- OS = Windows XP SP2 & Windows Vista
- 2 Mbps (1:2) leased line internet.
- Cyberoam C25i is acting as Router+Firewall+UTM

What steps shall i take?
Question by:VINOD MORE
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LVL 31

Accepted Solution

Frosty555 earned 75 total points
ID: 24371641
In general you shouldn't mess with it. Too big and it will exceed the MTU size of the physical network protocol, which forces the router to split packets unnecessarily. Too small and the packets get fragmented up too much.

1500 is the default. However PPPoE and some other devices sometimes choke on a number that big. To be safe, a lot of routers set the MTU size by default to 1492, which is just right.

In any case, as far as internet  browsing goes, MTU size will not affect performance. Internet is just too slow for it to matter. So don't mess with it unless you are experiencing network problems.
LVL 49

Assisted Solution

dbrunton earned 100 total points
ID: 24372151
LVL 10

Assisted Solution

lanboyo earned 50 total points
ID: 24374985
The only reason to change MTU is if you have or plan to have a lot of GRE or IPSec tunnels, or both.
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LVL 50

Assisted Solution

jcimarron earned 25 total points
ID: 24378468
vinodmore--This reference answers many questions and offers a tool (DrTCP) to help you determine the best settings for MTU, RWIN etc.

Author Comment

ID: 24381698
Thanks for comments

I have do this on Local systems (i mean DrTCP MTU settings) or on Router interface.

What is default MTU for Windows XP & Windows Vitsa?

LVL 49

Assisted Solution

dbrunton earned 100 total points
ID: 24381757
The default settings are in the link I gave above.  Usually 1500 but it may be necessary to drop according to circumstances.

Also see
LVL 10

Assisted Solution

lanboyo earned 50 total points
ID: 24383998
Dropping on the router interface only helps in the case of outbound traffic usually.

If you have no plans to tunnel through ipsec or gre tunnels or use pppoe, you really don't need to do anything.

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