[Vpn-help] MTU packet problems on Linux ...

Matthew Grooms mgrooms at shrew.net
Wed Dec 12 17:11:55 CST 2007


Matthew Grooms wrote:
> 
> I have been toying with the idea of making the virtual private network 
> adapter use an MTU of 1480 bytes. This could potentially make most of 
> these problems go away for the average user. Let me do some testing here 
> locally and if things look good, I will post a build. Would you be able 
> to test this for me with your adapter reset to the full 1500 byte MTU?
> 

I guess the adapter MTU would need to decrease to around 1396 bytes.

1500
-  8	PPPOE Header
- 20	IP Header
-  8	UDP Header
- 16	ESP Header
- 32	ESP IV Data ( estimated max )
- 16	ESP Padding ( estimated max )
-  1	ESP Pad Bytes
-  1	Next Protocol
-  2	Round to nearest 4 bytes
----
1396

Some trial and error would probably be in order.

-Matthew



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