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Re: [QUANTUM] (Bug ?) L3 routing not correctly fragmenting packets ?


Hi Sylvain,

This seems very odd to me. The reason this should happen is if your
client is sending packets with the DF (don't fragment) bit set in the
TCP header of the packets you are sending. I'd confirm that  your
version of 'curl' is doing this (which it should definitely not do!).
What should happen is the router should fragment the packets for you
and if a fragment is lost TCP will just re-transmit the full packet
again and things should eventually work....


On Fri, Mar 8, 2013 at 9:08 AM, Sylvain Bauza
<sylvain.bauza@xxxxxxxxxxxx> wrote:
> Hi,
> I recently observed a strange behaviour with L3 Quantum routing (Openvswitch
> setup with Provider Router). A simple curl to an external website is
> sometimes failing due to packet size  :
> > X.X.X.X: ICMP unreachable - need to frag
> (mtu 1454), length 556
>     IP (tos 0x0, ttl 48, id 25918, offset 0, flags [DF], proto TCP (6),
> length 1500)
> Only changing the VM MTU to 1454 does the trick ('ifconfig eth0 mtu 1454').
> For info, is the floating IP bound to (private IP).
> I can't provide the URL for reproducing, as the external website is actually
> an external corporate webservice.
> Do you have any idea on what could be the root cause, and how to fix it ?
> Thanks,
> -Sylvain
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