[ovs-discuss] SKB is modified 42 bytes in ovs module!help!

Jesse Gross jesse at nicira.com
Wed Apr 22 02:53:27 UTC 2015

On Tue, Apr 21, 2015 at 7:38 PM, wenxu <wenx05124561 at 163.com> wrote:
>>What does it mean that the packet is modified? What specifically happens?
> The VM sends a packet with 1500 bytes and the ovs will encapsulate the
> packet with gre tunnel and the packet length will larger than 1500. So the
> packet will be fragment to 2 packets. On the receiver side we find the last
> 42 bytes(user data) of the second packet was tampered by linux os.
> I think it's a matter with ovs and reassembly in linux kernel.  if we set
> the mtu of VM to 1458, the problem is gone.

You'll need to be specific about what happens to the second fragment.
Otherwise, there is no way for people to know where to start looking.
It would also be helpful if you look at the fragments on the wire to
see if anything unusual is happening (same IP IDs?).

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