[ovs-discuss] OVS/OVN troubleshooting: where's my packet?

Daniel Alvarez Sanchez dalvarez at redhat.com
Thu Mar 14 15:55:56 UTC 2019

Hi folks,

Lately I'm getting the question in the subject line more and more
frequently and facing it myself, especially in the context of

The shift to OVN in OpenStack involves a totally different approach
when it comes to tracing packet drops. Before OVN, there were a bunch
of network namespaces and devices where you could hook a tcpdump on
and inspect the traffic. People are used to those troubleshooting
techniques and OVS was merely used for normal action switches.

It's clear that there's tools and techniques to analyze this (trace
tool, port mirroring, etc.), but often times requires quite high
knowledge and understanding of the pipeline and OVS itself to
effectively trace where a packet got dropped. Furthermore, there could
be some scenarios where the packet can be silently dropped.

I came across this patch [0] and presentation about it [1] which aims
to tackle partly the problem described here (focusing in the DPDK

The intent of this email is to gather some feedback as how to provide
efficient tools and techniques to troubleshoot OVS/OVN issues and what
do you think is immediately missing in this context.

Thanks a lot!

[0] https://patchwork.ozlabs.org/patch/918934/
     which has been revived here: https://patchwork.ozlabs.org/patch/1048766/
[1] https://www.slideshare.net/LF_OpenvSwitch/lfovs17troubleshooting-the-data-plane-in-ovs-82280329

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