We're running Mitaka using OVS and I have been troubleshooting some MTU issues when I stumbled across this curiosity.
The VM OS in question has a interface MTU of 1500. When I do a tcpdump on the tap interface on the compute node that correlates to that VM, I see frames with a length of up to 10,000 bytes... Mostly I see frames that are up to 7300 bytes though. How is that possible per the VM that that interface is directly attached to has a MTU of 1500? Here's a snippit of a tcpdump from that VM's tap interface: [(openstack-mitaka) root@prv-0-18-compute user]# tcpdump -nni tap3bbe0f9d-6b src x.y.120.23 and dst x.y.224.45 tcpdump: WARNING: tap3bbe0f9d-6b: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on tap3bbe0f9d-6b, link-type EN10MB (Ethernet), capture size 65535 bytes 15:22:26.560455 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [S], seq 3200123597, win 65535, options [mss 1460,nop,wscale 2,nop,nop,sackOK], length 0 15:22:26.562741 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], ack 3169246826, win 53248, length 0 15:22:26.562853 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [P.], seq 0:36, ack 1, win 53248, length 36 15:22:26.563175 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 36:4416, ack 1, win 53248, length 4380 15:22:26.875289 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [P.], seq 0:1460, ack 1, win 53248, length 1460 15:22:26.876591 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 4416:10256, ack 1, win 53248, length 5840 15:22:27.781465 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 4416:5876, ack 1, win 53248, length 1460 15:22:27.782627 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 10256:17556, ack 1, win 53248, length 7300 15:22:30.484624 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 10256:11716, ack 1, win 53248, length 1460 15:22:30.486111 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 17556:24856, ack 1, win 53248, length 7300 15:22:35.203339 IP x.y.120.23.53540 > x.y.224.45.5001: Flags [.], seq 3585180775:3585182235, ack 1746533046, win 53248, length 1460 15:22:35.204632 IP x.y.120.23.53540 > x.y.224.45.5001: Flags [.], seq 7300:14600, ack 1, win 53248, length 7300 15:22:38.594013 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 17556:19016, ack 1, win 53248, length 1460 15:22:38.595570 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 24856:32156, ack 1, win 53248, length 7300 15:23:02.906420 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 24856:26316, ack 1, win 53248, length 1460 15:23:02.908021 IP x.y.120.23.53541 > x.y.224.45.5001: Flags [.], seq 32156:39456, ack 1, win 53248, length 7300 Any help on this would be appreciated! Steve
_______________________________________________ Mailing list: http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack Post to : [email protected] Unsubscribe : http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack
