It's hard to say, I would run tcpdump on each interface in the path and make sure that the packet is being fragmented at the place that you expect.
On Fri, Jan 24, 2014 at 5:50 PM, Zhou, Han <hzh...@ebay.com> wrote: > Hi Jesse, > > Thanks for your suggestion and now I can increase MTU of br-int after > increasing MTU of all other ports connected to it. > > However, after change MTU of br-int to 9000, I still get this same > fragmentation > (the GRE packet fragmentation, as you have explained) seen in tcpdump. > > I understand that generally I should set internal MTU smaller than physical > Interface so that tunnel headers are reserved. But in my ICMP testing the > packet size is only 1473 and I wonder where did this fragmentation happen? > > Now vnet interface, br-int, br0 and eth0 are all with MTU 9000, is there > any other point I should look at? > > Best regards, > Han > > -----Original Message----- > From: Jesse Gross [mailto:je...@nicira.com] > Sent: Friday, January 24, 2014 3:05 PM > To: Zhou, Han > Cc: discuss@openvswitch.org > Subject: Re: [ovs-discuss] Question on sending jumbo frames > > On Thu, Jan 23, 2014 at 5:32 PM, Zhou, Han <hzh...@ebay.com> wrote: >> Hi, >> >> I am using OVS2.0.1 and GRE tunnels for transport. >> I am trying to send jumbo frames from guest VM, so I changed MTU of VM's >> eth0, OVS interface br0, vport interface to the VM, and also host's eth0 to >> 9000. >> But I cannot change MTU of br-int with command ifconfig br-int mtu 9000. >> >> The results is that ping destination outside of the hypervisor with packet >> size >> larger than 1472 fails. tcpdump -i br0 captures truncated packets: >> ... GREv0, key=0xb5515, seq 9400832, length 1480: IP truncated-ip - >> 54 bytes missing! 11.11.11.4 > 11.11.11.2: ICMP echo request, id 1416, seq >> 3044, length 1488 > > I believe that what you are seeing is fragmentation, not a truncated > packet. tcpdump only sees part of the IP packet in the GRE payload but > there should be another GRE fragment that follows. Even with jumbo > frames, the VM's MTU should still be lower than the physical network's > to account for tunnel headers. > > The MTU of the internal device is restricted to be no more than the > smallest MTU of the attached devices on the bridge so I would check > that you have updated all of the other MTUs first. _______________________________________________ discuss mailing list discuss@openvswitch.org http://openvswitch.org/mailman/listinfo/discuss
