Hi, On Tue, 2014-05-13 at 07:00 +0000, Yinpeijun wrote: > >> >Subject: Re: [ovs-discuss] VXLAN problems > >> >To: Jesse Gross <je...@nicira.com> > >> >Cc: "discuss@openvswitch.org" <discuss@openvswitch.org> > >> >Message-ID: > >> > > >> ><cafiynd8qd7eu4sv2eoljxka0k05k-ns+ag0reaeudgacejk...@mail.gmail.com> > >> >Content-Type: text/plain; charset="iso-8859-1" > >> > > >> >I managed to solve this by setting VM NIC MTU to 1400, 1450 wasn't enough. > >> > > >> >Thanks. > >> > >> Hello ,I use ovs-2.0.0 and test vxlan scp between two VMS,and find the > >> same problem¡£ > >> > >> but I think change VM NIC MTU is just avoid and has not solve the > >> problem¡£I want to > >> > >> know we have to change VM NIC or PHY NIC MTU when we use vxlan to > >> communication ? > >> > > > >This is due to the tunnel outer header that adds VXLAN + UDP + IP + ETH = 50 > >bytes to the inner packets. When TCP stream is tested between VMs, TCP > >buffer is segmented to 1500 bytes, but with outer header added, it will be > >1550 that slightly exceed PHY NIC MTU, and results in an additional IP > >fragmentation into big + small packet pairs in Hypervisor's IP stack. > > > >In my environment configuring VM MTU to the same as PHY NIC MTU (1500) leads > >to 40% performance drop. > > > >Does this answer your question? > > > >Best regards, > >Han > > Thank you for your reply ,Han. I agree with your analysis and know the > process , My confusion is, whether to have clear documentation or rules that > PHY or VM NIC MTU need to be modified when we use > > ovs vxlan to communication ? > > > if needed, we should increase PYH NIC MTU or decrease VM NIC MTU ? >
This problem exists also on other tunnel protocols such as GRE. We should always increase PHY NIC MTU when possible. In fact, MTU specified by VM doesn't make any sense in a virtualized environment. Maybe you can try this patch if you are interested: http://openvswitch.org/pipermail/dev/2014-May/040027.html You don't need to care about VM MTU setting with this patch, and the best thing is that it will be much faster even comparing with properly changed MTU. Best regards, Han _______________________________________________ discuss mailing list discuss@openvswitch.org http://openvswitch.org/mailman/listinfo/discuss
