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PIM Assert: Potential for routing loops?

Hi all

I've read in the 'IP Multicast Best Practices for Enterprise Customers' whitepaper that Assert can cause issues which states the following:

"Assert issues

The PIM Assert mechanism prevents duplicate traffic from flowing into a multi-access network. Assert messages are sent by the two forwarding routers and the router with the best metric will win the assert. There are several known cases in which assert can cause temporary routing loops and sub optimal behavior."

At the moment I have 3 x routers in PIM-SM that talk Auto-RP and in a packet capture I am seeing many assert messages. I understand Assert is only used in Dense-mode, however Auto-RP floods in Dense mode to 224.1.0.39(RP-ANNOUNCE) & 224.1.0.40(RP-DISCOVER), which are the 'groups' my routers are trying to assert over.

We have had some issues in which Auto-RP traffic has been amplified in our carrier network and I'm trying to understand if the PIM Assert process could have a hand in that.

As a starting point, can anyone offer insight into how PIM Assert has the potential to cause routing loops?

Thanks

 

 

 

 

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