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  • 1.  Multiple Paths for PIM

    Posted 02-19-2024 22:51

    I have the following topology

    I have BGP peers between L3-SW and RF routers on two sides. RP is configured on RF routers with the same IP. When PIM is enabled on both L3 switches, PIM always works on L3-SW-B path. If I shutdown the uplink on L3-SW-B,  mcast traffic stops until I deactivate PIM on L3-SW-B.

    If I deactivate PIM on L3-SW-B, mcast traffic can flow via L3-SW-A.

    Anyone can show me how I can fail over to L3-SW-A path with deactivating PIM on L3-SW-B ?
    thanks !!


  • 2.  RE: Multiple Paths for PIM

    Posted 02-19-2024 23:50

    Does assert deal with this case ?


    Original Message


  • 3.  RE: Multiple Paths for PIM

    Posted 02-20-2024 11:58

    In this case (multiple mrouters in a single VLAN), IGMP Election is the point. When you activate PIM, IGMP is activated too:

    «IGMP DR and Querier are selected by an election. The router with highest IPv4 address becomes the DR and the router with lowest IPv4 address becomes the IGMP Querier.»

    The IGMP DR will listen to group join/leave and will join the group on the PIM/backbone side.



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    Olivier Benghozi
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    Original Message


  • 4.  RE: Multiple Paths for PIM

    Posted 02-21-2024 10:34

    thanks a lot !!
    In my case. the left side is DR based on its high IPs, so the traffic flows via the left side. when I changed PIM interface priority, I can shift the traffic flow to the right side.

    Both uplinks are nonDR as they are not in a share network.

    My question is how and when  the uplink on DR side fails, the multicast traffic automatically fails over to the other side.  

    Currently in my lab, multicast traffic flow stops as DR does not shift to the other side.

    I am thinking to update PIM interface priority via event script. 

    Anyone has better ideas ?

    thanks a lot !!


    Original Message


  • 5.  RE: Multiple Paths for PIM

    Posted 02-21-2024 09:37

    You mentioned, "If I shutdown the uplink on L3-SW-B,  mcast traffic stops".  It would be interesting to see ....

    PE, RF-1, RF-2...
    show pim join
    show multicast route

    L3-SW-A and B....
    show igmp groups
    show igmp snooping membership

    ...before, during, and after your problem of "If I shutdown the uplink on L3-SW-B,  mcast traffic stops"

    I wonder if the multicast tree is built in such a way that you have then broken the path during the shutdown of the uplink on L3-SW-B, and the multicast tree isn't re-built on the remaining path... maybe there is a way to speed up this awareness and reconvergence.  Also, I'm wondering if there are any static unicast routes that would prevent auto-reconvergence to take place 



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    - Aaron
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    Original Message


  • 6.  RE: Multiple Paths for PIM

    Posted 02-21-2024 10:36

    thanks a lot !!


    Original Message