how to change MTU size in OpenVPN Access Server

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marcb_ro
OpenVpn Newbie
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Joined: Fri Sep 09, 2011 9:22 pm

how to change MTU size in OpenVPN Access Server

Post by marcb_ro » Fri Sep 09, 2011 9:36 pm

Hello, world!

I've successfully deployed an openvpnas, and i can can connect to it from 3 different ISPs using both TCP and UDP connections. I'm only using Linux clients, as I have long abandoned windows (too many flaws).

However, when trying to connect from an computer hooked up to the internet by an ISP that uses PPPoE, I cannot establish a tunnel between the two computers, as the MTU size for PPPoE is set to 1492 and the server expects 1500, so packages of 1500 bytes cannot travel over the PPPoE link restricted to 1492 bytes. If I set the max MTU to 1492 on the client I get the following:

Code: Select all

2011-09-09 22:59:01+0300 [-] OVPN 0 OUT: 'Fri Sep  9 19:59:01 2011 IP:port WARNING: 'link-mtu' is used inconsistently, local='link-mtu 1544', remote='link-mtu 1536''
2011-09-09 22:59:01+0300 [-] OVPN 0 OUT: 'Fri Sep  9 19:59:01 2011 IP:port WARNING: 'tun-mtu' is used inconsistently, local='tun-mtu 1500', remote='tun-mtu 1492''
2011-09-10 00:31:04+0300 [-] OVPN 0 OUT: 'Fri Sep  9 21:31:04 2011 IP:port Option inconsistency warnings triggering disconnect due to --opt-verify'
I can set MTU max length on the clients, but I also need to do it on the server. I would very much appreciate any help I. I am open to your suggestions.

Have a good one!

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Andrew
OpenVPN Inc.
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Joined: Mon Oct 05, 2009 11:52 pm
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Re: how to change MTU size in OpenVPN Access Server

Post by Andrew » Mon Sep 19, 2011 11:45 pm

Hello,

You will want to use the mssfix directive under Admin UI>Advanced VPN Setting>Server Config Directives.
Andrew Proctor
OpenVPN Technologies
http://openvpn.net

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