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[Openvpn-users] MTU questions

  • Subject: [Openvpn-users] MTU questions
  • From: "Brent P. Gardner" <bgardner@xxxxxxxxxxxx>
  • Date: Wed, 08 Dec 2004 13:05:53 -0700 (MST)

I'm evaluating OpenVPN as a solution for our road warriors.  On the 
server side I run v1.6, v2.0rc1 on the client side.  I have a question 
about log entries such as the following which shows up on either side 
of the connection:

  Control Channel MTU parms [ L:1578 D:138 EF:38 EB:0 ET:0 EL:0 ]
  Data Channel MTU parms [ L:1578 D:1450 EF:46 EB:19 ET:32 EL:0 ]
  Fragmentation MTU parms [ L:1578 D:1450 EF:45 EB:19 ET:33 EL:0 ]

Does this mean that MTU for the connection has been set to 1578?  The 
L: value is always 78 greater than what I put for tun-mtu in the 
config files.

Also, I occaisionally see entries in the server log in the form of:

  MSS: 1460 -> xxxx

where xxxx is some value less than 1460.  Does this mean that the MTU 
is being dynamically optimized for the connection?  Should I lower 
the MTU settings in my config files to match what shows in the logs?


Brent Gardner
Network Administrator
IPRO Tech, Inc.

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