--fragment --mssfix Confusion

pada123

Hi All , I am in the process of setting up a VPN server which will be used by multiple clients.

currently I have UDP mode only

In server I have not changed any settings related to MTU . It means MTU size is 1500.

Now It may be the case for one client MTU is 1500. So Its ok..But for another client his network permits say MTU 1024 only

So here How can I set different MTU size for different different clients keeping MTU fixed 1500 at server side.

I got following from Forum
=================================
1>>
<<<
--fragment 1468 tells OpenVPN to never attempt to send a UDP packet larger
than 1468. --mssfix 1468 tells the TCP layer to use an MSS that may be
smaller than 1468. >>>>

2>> Note that while mssfix only needs to be specified on one side of the connection, fragment should be specified on both.
==================================

As I am using UDP mode , I need to use --fragment.
But as per forum post I need to set it both client and server side also..So it means for few clients who have less MTU I am effecting those who have big 1500 MTU without issue as well Server has also MTU 1500.

Pls help me to understand.

I need something like..I want to keep MTU 1500 default in server...and for every client they can enter some option in client config file as per their MTU size.

Thank you
pada

Mimiko

You can set in server the MTU to smallest value which some client can have and set this MTU to all clients. Or set to all clients MTU to default wich will permit the clients to work, only that the client with MTU 1024 will have to fragment packets in order to send VPN packets to server.

pada123

Thanks Mimiko for your Input. But I am not very clear.

Setting small MTU permanently in server will hamper the speed ,Where server and many client have 1500 MTU..

So for those clients who have smaller MTU ..CAN I set any thing in client config ..So that that smaller MTU will be applicable.

Like Smallest MTU between server and Client will take effect.

Pls give me light.
Thank you
Pada

Mimiko

You can use "--link-mtu" and "--mtu-test".

pada123

Thanks Mimiko.
It means
Keeping server default value 1500 I will only set in client config --link-mtu 1024 or smaller for those clients who have less MTU.

when they will connect say 1024 will take effect and for other who do not set anything default 1500 will take effect.

Am I correct Mimiko.
Thank You
Pada