How to do packet capture (tcpdump) of contrail LB VIP and its backend traffic flow. 

While troubleshooting data plane issue related to contrail LB services, there will be a need to do packet capture (tcpdump) of contrail LB VIP

Login to the vRouter where the LB instance is created and running.
Use contrail-tools command and identify the veth interface created and consumed by the LB service.
run vif dump of the veth interface to monitor the LB traffic.
Additionally list the netns created by contrail on the compute node as part of LB instantiation.