[Openvpn-users] A question about UDP encapsulation with OpenVPN 2.0.x

[Attilio Fiandrotti <fiandro@xxxxxxxxxx>]

Hi

i'm doing some test to evaluate performance of openvpn over ethernet links.
I'm running ovpn 2.0.7 on linux intel, i'm using UDP encapsulation and 
p2p mode and, for testing purposes, i disabled both compression and 
crypto over the tunnel.

Now, let's pretend i want to send an ICMP ECHO message over the tunnel, 
like this (measurements are in bytes)

ICMP data                      56 +
ICMP ECHO header                8 =
----------------------------------
                                64 +
IP header                      20 =
----------------------------------
UDP payload                    84 +
UDP openvpn encapsulation       8 =
----------------------------------
                                92 +
IP openvpn encapsulation       20 =
-----------------------------------
IP packet sent over tunnel    112

at the other end of the tunnel, i should receive a 112 bytes big ip 
packet, but instead i receive a 137 bytes long packet, and using 
etherreal i noticed UDP payload is 119 bytes instead of 84.
Now, i'm sure i'm mising something about openvpn udp encapsulation 
mechanism: what are the unexpected bytes for? what do they contain ? 
where can i find documentation about openvpn internals ?

thanks a lot!

attilio

ps

please, CC me in reply as i'm not subscribed to this list
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