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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">You can narrow down the point where the packets are being dropped by mirroring and tracing packets on OVS bridge ports. I use a script that does the following
(as root):<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ip link add name sniff0 type dummy<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ip link set dev sniff0 up<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ovs-vsctl add-port br1 sniff0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ovs-vsctl -- set Bridge br1 mirrors=@m \<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-- --id=@sniff0 get Port sniff0 \<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-- --id=@eth0 get Port eth0 \<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-- --id=@m create Mirror name=mirror0 \<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">select-dst-port=@eth0 select-src-port=@eth0 \<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">output-port=@sniff0 select_all=1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">and to delete,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ovs-vsctl clear Bridge br1 mirrors<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ovs-vsctl del-port br1 sniff0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ip link del dev sniff0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">where eth0 is the point of packet capture and br1 is the bridge eth0 resides in. Then, you can run tcpdump on sniff0.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Create such mirror ports on
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">1) phy-br-ex on external OVS bridge<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">2) int-br-ex on integration bridge<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">3) qvo-xxx on integration bridge<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Also capture packets on qvb-xxx on the linux bridge having the tap interface of the VM. Hopefully, this will provide us more clues.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">-Kaustubh<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Sterdnot Shaken [mailto:sterdnotshaken@gmail.com]
<br>
<b>Sent:</b> Monday, March 20, 2017 9:17 PM<br>
<b>To:</b> Richard Jones <rjones@suse.com><br>
<b>Cc:</b> openstack@lists.openstack.org<br>
<b>Subject:</b> Re: [Openstack] VM can receive traffic, but not send it<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Wow! Thanks for answering both of my questions!<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">So, I did some things you suggested, including setting the MSS in iperf to something small (1000 bytes) and tested with no improvement. I then changed the VM running on Openstack to have an MTU of 1000 and retested
with no improvement. I noticed that the node I was testing against was reporting back to the VM on Openstack that it had an MSS of 8960, so just for the heck of it, I changed the remote node's (server outside of Openstack) MTU also to 1000 bytes and retested
with no improvement. (The effects of all of these tests were also validated by checking mss settings in the tcp header via tcpdump).<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">To simplify the equation, I ditched the iperf for the time being and just did a simple "telnet 'remote server' 8080" test from the remote server to the VM in Openstack, while capturing packets all along the
way (4 different points along the network path). Every point saw the same packets, including the VM's tap interface as expected. I then reversed the test by initiating the tcp session on the VM in Openstack to the remote server while running the packet captures
at those same points having set the remote server to respond with a TCP Reset. From VM to Remote server traffic looked correct with expected TCP SYN. The TCP Reset that the remote server responded with passed all 4 points of the network, including the external
interface on the Compute node where the VM resides, but the TAP interface that connects to the VM NEVER sees the Reset. I can recreate this condition over and over.
<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">So, thanks to your ideas Richard, I'm no longer convinced this is an MTU issue. What would prevent a TCP related response from being forwarded from the external interface to the intended VM? The security group
we have applied to this VM is wide open, so I can't imagine that is the cause...
<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Here are 2 packet captures where I initiated a telnet to the remote server from the VM in Openstack. As said above, I set the remote server to respond with a reset. The top one is from the physical interface
on the Compute node where the VM resides and the other, the tap interface to that VM:<br>
<br>
[(openstack-mitaka) root@prv-0-18-compute user]# tcpdump -nni eth0 host x.y.120.23 and host x.y.224.45<br>
tcpdump: WARNING: eth0: no IPv4 address assigned<br>
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode<br>
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes<br>
19:10:13.143931 IP x.y.120.23.53877 > x.y.224.45.8080: Flags [S], seq 3131027441, win 8192, options [mss 960,nop,wscale 8,nop,nop,sackOK], length 0<br>
19:10:13.147951 IP x.y.224.45.8080 > x.y.120.23.53877: Flags [R.], seq 0, ack 3131027442, win 0, length 0<br>
19:10:16.156520 IP x.y.120.23.53877 > x.y.224.45.8080: Flags [S], seq 3131027441, win 8192, options [mss 960,nop,wscale 8,nop,nop,sackOK], length 0<br>
19:10:16.157693 IP x.y.224.45.8080 > x.y.120.23.53877: Flags [R.], seq 0, ack 1, win 0, length 0<br>
19:10:22.157407 IP x.y.120.23.53877 > x.y.224.45.8080: Flags [S], seq 3131027441, win 8192, options [mss 960,nop,nop,sackOK], length 0<br>
19:10:22.158682 IP x.y.224.45.8080 > x.y.120.23.53877: Flags [R.], seq 0, ack 1, win 0, length 0<br>
<br>
<br>
[(openstack-mitaka) root@prv-0-18-compute user]# tcpdump -nni tap3bbe0f9d-6b host x.y.120.23 and host x.y.224.45<br>
tcpdump: WARNING: tap3bbe0f9d-6b: no IPv4 address assigned<br>
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode<br>
listening on tap3bbe0f9d-6b, link-type EN10MB (Ethernet), capture size 65535 bytes<br>
19:10:13.143739 IP x.y.120.23.53877 > x.y.224.45.8080: Flags [S], seq 3131027441, win 8192, options [mss 960,nop,wscale 8,nop,nop,sackOK], length 0<br>
19:10:16.156499 IP x.y.120.23.53877 > x.y.224.45.8080: Flags [S], seq 3131027441, win 8192, options [mss 960,nop,wscale 8,nop,nop,sackOK], length 0<br>
19:10:22.157384 IP x.y.120.23.53877 > x.y.224.45.8080: Flags [S], seq 3131027441, win 8192, options [mss 960,nop,nop,sackOK], length 0<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Any ideas? Thanks in advance for your help!!<o:p></o:p></p>
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<p class="MsoNormal">Steve <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Mon, Mar 20, 2017 at 4:17 PM, Richard Jones <<a href="mailto:rjones@suse.com" target="_blank">rjones@suse.com</a>> wrote:<o:p></o:p></p>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in">
<p class="MsoNormal">You might consider taking a packet trace of the start of an upload to see what the TCP MSS (Maximum Segment Size) options look like and perhaps compare between the different configs. Also, you could consider either using netperf and having
it tweak the MSS to a smaller value (test-specific -G option if I recall correctly), or just try dropping the MTU of your VM before you try the upload.<br>
<br>
Another way to use netperf to "probe" without tweaking MSS or MTU settings would be to use the TCP_RR test with increasing request/response sizes. If there is indeed an MTU issue somewhere along the way, as you walk the request/response size up to the local
MTU, you should see the test performance drop off a cliff if not go fully to zero.<br>
<br>
Does the port for the VM have a security group rule permitting ICMP traffic in? Offhand I wouldn't expect that to be different between the two network setups you've described because I'd not have expected the virtual router to pay attention to an arriving
ICMP Destination Unreachable, Datagram Too Big message to have the routed version work, but it seemed a reasonable straw at which to grasp.<br>
<br>
rick jones<br>
<br>
PS perhaps iperf has a similar option to set the TCP MSS, I've not looked.<br>
<br>
>>> Sterdnot Shaken <<a href="mailto:sterdnotshaken@gmail.com">sterdnotshaken@gmail.com</a>> 03/20/17 3:07 PM >>><o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Our info:<br>
<br>
Openstack version: Mitaka (using OVS 2.5)<br>
Firewall driver: Openvswitch<br>
<br>
Anyone know why VM's that are directly on a Flat Provider Network (so the<br>
VM would have a public IP directly assigned to it) can download data just<br>
fine, but when we try and upload anything (iperf where the VM is the client<br>
or something even like <a href="http://speedtest.net" target="_blank">speedtest.net</a> (upload portion)) the VM simply can't<br>
get data out to the intended destination? Again, download works great,<br>
upload doesn't.<br>
<br>
If I take that VM and change it's interface to be a tenant network one that<br>
has a Openstack HA virtual router, everything (upload and download) works<br>
perfectly. The problem only seems to be apparent when the VM is directly on<br>
the external network.<br>
<br>
It seems like an MTU issue, but I don't see how... Here are the MTU's of<br>
the part's at play:<br>
<br>
VM: 1500<br>
br-int (specific interface connecting to VM) - 9216<br>
br-ex - (can't tell what that MTU is set to)<br>
<br>
Any help would be GREATLY appreciated.<br>
<br>
Steve<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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