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Re: [Openvpn-users] how to reduce tunnel bandwidth usage caused by abnormal packet overhead


  • Subject: Re: [Openvpn-users] how to reduce tunnel bandwidth usage caused by abnormal packet overhead
  • From: Jan Just Keijser <janjust@xxxxxxxxx>
  • Date: Sat, 26 Jan 2008 00:04:29 +0100

Hi Mohammad,

an encapsulation overhead of 36 -> 101 bytes does not seem too bad to 
me. Esp with small packets the "extra" overhead of encapsulation always 
seems bad. Try disabling compression (no-comp-lzo) to see if that gains 
you anything. Compression does not make much sense for packets this 
small and is likely to cause an *increase* in packet size instead of a 
decrease.
And yes, TLS handshaking will also add some overhead. There are no other 
options to reduce tunnel overhead.

HTH,

JJK

Mohammad Reza Saghaei wrote:
> I am using OpenVPN to handle voice traffic over Internet and I want to 
> reduce my tunnel bandwidth usage.I use UDP tun mode and everythings 
> seems to be working fine except huge bandwidth usage which is abnormal 
> I think.
> I used tcpdump to check my udp packet sizes through interface tun0 and 
> the resault is all like this:
> 12:46:35.452412 IP xxx.xx.63.214.29014 > xxx.xx.99.11.24510: UDP, 
> length 36
> 12:46:35.462336 IP xxx.xx.63.214.29010 > xxx.xx.99.11.24902: UDP, 
> length 32
> 12:46:35.466547 IP xxx.xx.99.11.24364 > xxx.xx.63.214.29004: UDP, 
> length 32
> 12:46:35.482370 IP xxx.xx.63.214.29014 > xxx.xx.99.11.24510: UDP, 
> length 36
>  
> the I checked the same thing over interface eth0 which is tunneled udp 
> packets including tunneling overhead I think and this is the resault:
> 12:51:46.302306 IP xxx.xxx.231.162.5002 > xxx.xxx.19.2.32771: UDP, 
> length 101
> 12:51:46.302337 IP xxx.xxx.19.2.32771 > xxx.xxx.231.162.5002: UDP, 
> length 77
> 12:51:46.304045 IP xxx.xxx.231.162.5002 > xxx.xxx.19.2.32771: UDP, 
> length 101
> 12:51:46.311468 IP xxx.xxx.231.162.5002 > xxx.xxx.19.2.32771: UDP, 
> length 101
> 12:51:46.312140 IP xxx.xxx.19.2.32771 > xxx.xxx.231.162.5002: UDP, 
> length 101
>  
> So it seems that there is no MTU related problem because packet sizes 
> are very small and not even anything near to 14xx/1500.
> but why my tunneled packet sizes become 3 times larger than original 
> ones?! and how can I reduce the overhead to its least possible to 
> lower my requiered bandwidth usage.I searched your archive and could 
> find nothing.
> please help me and tell me what are my detailed udp packets overhead 
> and how can I modify them?
> I use TLS handshaking and this is one of my clients config file:
> client
> dev tun
> proto udp
> remote xxx.xxx.231.162 5002
> resolv-retry infinite
> nobind
> user nobody
> group nobody
> persist-key
> persist-tun
> ns-cert-type server
> ca /etc/openvpn/keys/ca.crt
> cert /etc/openvpn/keys/client2.crt
> key /etc/openvpn/keys/client2.key
> comp-lzo
>  
> thank you,
>
>  
>  

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