It's sheer coincidence that that posts are only 10 min apart. In my setup all interfaces have MTU defined to be 1500 before I applied the workaround.
I tried to do tcpdump on the client to see if the frames received are over 1516 and ip pkts over 1500... Nope Will try a simple linux bridge and see. Thanks. Sent from my iPhone > On Jun 23, 2015, at 7:16 PM, Jesse Gross <je...@nicira.com> wrote: > >> On Fri, Jun 19, 2015 at 1:52 PM, Johnson L. Wu <john...@snoopy.org> wrote: >> >> >> Greetings, >> >> >> >> I am currently running >> >> 3.16.0-4-amd64 >> >> No LSB modules are available. >> >> Distributor ID: Debian >> >> Description: Debian GNU/Linux 8.1 (jessie) >> >> Release: 8.1 >> >> Codename: jessie >> >> ovs-vsctl (Open vSwitch) 2.3.1 >> >> Compiled Jun 15 2015 19:30:36 >> >> DB Schema 7.6.2 >> >> libvirtd (libvirt) 1.2.9 >> >> >> >> and I am seeing an MTU issue where packets coming in from the physical side >> are vanilla 1500Bytes >> >> Once it gets to the virtual NIC I see the following in dmesg: >> >> >> >> [ 6754.472356] openvswitch: vnet5: dropped over-mtu packet: 1502 > 1500 >> >> [ 6754.472363] openvswitch: inter-1tom: dropped over-mtu packet: 1502 > 1500 >> >> >> >> If I set BOTH the vnet5 vnic to mtu 1502 AND the guest OS MTU to 1502 things >> will flow >> >> Otherwise mant protocols with full sized packets will see timeout. >> >> >> >> Wireshark loaded on the client didn’t help, as a trace done on the client >> itself sees the IP packets coming in (AFTER adjusting MTU to 1502) as 1500. >> >> >> >> I think OVS must be doing something that added a tag to the packets. >> >> Anyone with the same observation? > > I've never heard of this problem before and there were two threads > started on it within 10 minutes, so I'm combining them together on the > assumption that they are somehow related. > > It's not really obvious to me how or why OVS would be increasing the > size of the packet by 1 or 2 bytes, especially if the packet is just > flowing through. As I said, I've never heard this reported before. In > the other message, it looks like OVS should be removing a VLAN tag. Is > that true in both cases? > > Similarly, in the other thread, it looks the MTUs of the physical > interfaces are 9000, which makes it seems like it is possible that > these packets are actually coming across the wire. What happens if the > MTUs are all the same, as required by Ethernet specs? > > Finally, it would be helpful to try this with the Linux bridge instead > of OVS, if possible, since it seems likely that the cause may be > another component. _______________________________________________ discuss mailing list discuss@openvswitch.org http://openvswitch.org/mailman/listinfo/discuss
