Re: multicast-transition

[Dino Farinacci <dino@procket.com>]

>> The first multicast aware router along the path notices the message
>> and creates a tunnel to the source address in the IP header.

    In most cases, a router doesn't know it is the first multicast router.
    With topology changes, you need the Join to be sent periodically so
    it can time out the tunnel state in the multicast router.

    Also this is not trivial to do in existing hardware from the multicast
    router's point of view. When a router is in it's replication loop, there
    are no changes to the IP header, just changes to the layer-2 header.

    This solution requires the destination IP address to be rewritten and
    an entire IP header checksum recalculation (partial checksum will be
    hard in this case). You effectively put NAT in the fast-path.

    So simple as it may seem, it really isn't.

Dino