In codfw, HTCP purge traffic (multicast traffic) is being sent in most of our networks. For example Parsoid codfw boxes get HTCP purge traffic. That is due to the switches broadcast (instead of multicast) to all of the boxes the HTCP traffic. It suffices that one box in an entire switch joins the multicast purge group and all boxes on that switch start getting the traffic. The solution is known and old. IGMP snooping. Up to junos 13.2 the default was to enable igmp-snooping on all vlans. However we are in 14.1 and that no longer holds true, hence it seems that we need to configure igmp snooping manually. Doing that is easy however it seems to break IPv6 multicast, breaking RA advertisements and hence IPv6 connectivity. That used to be a bug in the EX series but it reportedly has been fixed years ago. Not sure if it would make its resurgence in QFX5100. At the same time MLD snooping, the IGMP snooping equivalent in the world of IPv6, would solve the problem as well, and in fact it is the preferred solution, but while EX series seems to support, the QFX series seems to not yet.
Need to investigate this further and manage to enable IGMP snooping in codfw without breaking IPv6.
 Note: IGMP snooping is enabled by default on the default VLAN only. With versions of Junos OS for the QFX Series previous to 13.2, IGMP snooping is enabled by default on all VLANs. https://www.juniper.net/documentation/en_US/junos14.1/topics/concept/igmp-snooping-qfx-series-overview.html