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:[email protected]] Sent: Friday, January 24, 2014 3:05 PM To: Zhou, Han Cc: [email protected] Subject: Re: [ovs-discuss] Question on sending jumbo frames On Thu, Jan 23, 2014 at 5:32 PM, Zhou, Han <[email protected]> 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 [email protected] http://openvswitch.org/mailman/listinfo/discuss
