Multiple candidate RPs

Hi all,

I was working on IEWBvol1 Multicast section and came across page.64 where a design with multiple RPs was discussed.

I've yet to figure out why (and how) the logic works...I think these two sentences look somehow contradictory: (copy and paste from the text)

1- "For overlapping ranges MA will only advertise the RP with the highest IP address"

2- "Notice that the mapping list is copiles by the MA but still the final RP selection is performed by multicast routers." <the longest match criterion>


As you see it's not clear that whether both or just one of the candidates would be offered to routers in the network. So if for a particular range I introduce more than one cRP who's gonna be the actual RP?






  • They both are true, I'm sure if you read it again you will see why.

    I'll try to give an example:

    RP 1 - --> mapped to 2 ranges, and

    RP 2 - --> mapped to 2 ranges, and


    Because the MA advertises only one RP for an overlapping range, only RP2 will be advertised for the entire multicast range.

    RP1 will be advertised for range 224- and RP2 will be advertised for range 232- and range 224-

    The multicast routers will choose to use RP1 for the first range because it is the longest match.

    The point of all this is that if one of the RPs fails, the other can take over for the entire range, while at the same time load balancing during normal operation.


    If I am right above, then the word 'overlapping' is not really the best to use, 'identical' would be better?

    Otherwise someone please correct me :-)


  • Thanks very much Nikola.




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