The article explains about the issue when EX9208 becomes a PIM DR in 19.1 releases.

Let us take the example where the EX9208 acts as super spines in EVPN VXLAN CRB Fabric. The multicast source is outside the fabric.

The Leaf devices send the interested IGMP joins from subscribers to the EX9208 as type-6 EVPN routes.

When the EX9208 is made a PIM DR, it is expected that the multicast traffic to be routed to interested subscribers.

root@Spine-EX9208# show | compare 

[edit routing-instances TEST protocols pim interface irb.1515]

+     priority 2;

{master}[edit]

But when the EX9208 becomes PIM DR, it appears to flood the multicast traffic to all the interfaces that are part of the bridge domain. All multicast subscribers and non-subscribers will receive bogus multicast traffic. Without capturing any packets, it would appear as if the non-subscribers were receiving multicast traffic.

But only part of the subscribers will be receiving the actual multicast traffic. Most of the multicast subscribers and non-subscribers will receive the bogus multicast packet. It is generated by the EX9208 which became a PIM DR.

The bogus multicast traffic would have unknown source mac with unknown ether-type. Sample copy of the bogus multicast packets is below.

There is no solution for this release. Customer needs to upgrade to latest recommended version.