traffic not going through tunnel

[Soeren Malchow]

Dear all,

we have a very strange problem, 

- we have 3 VPN endpoints
- all are in one NETWORK
- all daemons come up and connect without any problem and normally we have no problem working through the VPN

but in some cases the connection does not work because the traffic leaves the TAP interface on one VPN endpoint but never arrives on the other end, the similarities between the packages seem to be

- the packages are 1500 bytes long ( lower MTU does not solve the problem )
- the packages have no checksum
	16:26:25.982932 IP (tos 0x0, ttl 127, id 19831, offset 0, flags [DF], proto TCP (6), length 1500) XXX.XXX.XXX.XXX.443 > XXX.XXX.XXX.XXX.51285: . 512:1960(1448) ack 1200 win 64163 <nop,nop,timestamp 249076008 754904913>

does anyone even have a suggestion where to look, we have no further ideas how to solve that

thanks in advance
soeren