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Multicasting/PIM SM doubts


I am novice in multicasting.

I have few question relating to multicasting & PIM-SM concepts.

1. Who will assign multicasting group addresses? Is it assigned through IANA??

Does that mean now we have only multicast group from to ?

I wonder only these many multicast group exist in the world.

2. How big is PIM-SM domain?

These multicast routing protocol doesnot talk about any Inter-domain & Intra-domain things.

So does this mean that PIM-SM domain spreads through out the internet?

If not, how is Inter-domain multicast routing done?

If yes, only one Bootstrap router exist through out Internet?

Can anyone clarify these questions? You might feel these questions are silly. But I am a novice & just starting

off in multicasting things. Please let me know if I am wrong anywhere.

Thanks in advance,


New Member

Re: Multicasting/PIM SM doubts

Hi Srinivas,

I have experience of running PIM-SM on our LAN. I don't know about assigning multicast addresses on a WAN, but in a LAN, you as the network administrator should assign multicast groups to users.

You have correctly stated the address range of multicast groups, but you have to be very careful when assigning them. Basically, there is a 2^5 address ambiguity at the MAC address layer so many multicast IP addresses map to the same multicast MAC address. You should aim to assign addresses such that each multicast IP has a unique multicast MAC address. The other thing to watch out for when assigning multicast IP addresses is that they don't map to any of the IANA reserved addresses at the MAC level.

Sorry, I can't answer your second question, as I'm new to networking.

Hope this helps,


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