Re: [pim] Simple join failure notification for PIM-SM multicast routing

[Dino Farinacci <dino at cisco.com>]

>> "Currently, PIM-SM is the most widely deployed multicast routing
>> protocol in the Internet. However in IPv6 this multicast protocol
>> lacks a simple connectivity debugging tool, making it difficult to
>> identify multicast routing problems.  When a host wants to receive a
>> multicast group or channel, if the corresponding  PIM-Join message
>> cannot be propagated in the network, nothing exists to inform the
>> receiver or the network about this failure. We propose a simple error
>> notification message based on ICMP/ICMP6 which is able to indicate
>> where and why the error happened in the network without using a
>> multicast traceroute mechanism."

    IP multicast scales well today because no where in the network state is
    maintained per receiver. This is an important scalability principle I
    would like to see not change.

    What happens if a link goes down where it affects 1000s of receivers.
    The router on the downstream side of the failure would 1) have to track
    the receivers and 2) send a message to each of them. This can't possibly
    be workable. 

    This should be solved and there are cases where it has been solved by
    doing beaconing at the application layer.

Dino

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