| Multicast Blog |
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| Monday, 03 November 2008 09:24 |
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&q
Is PIM Dense Mode Really Dead?
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According to everyone inside Cisco at the latest 2008 Networkers conference dense mode PIM is definitely considered a legacy protocol. That is what I also have been hearing for the last five years or so, but that does not mean that dense mode is still not in use in the field.
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(I am not talking about "sparse-dense" which was specified by many Cisco consultants for Auto RP implimentations prior to IOS version 12.2. In 12.2 the auto rp listener command was introduced so now the Auto RP process can work in sparse mode on the interfaces instead of sparse-dense mode. If sparse mode is used one avoids dense mode flooding. Sparse-Dense will be the subject of another blog entry.)
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No, I am talking about pure dense mode. The one industry I still see it is in Cable TV. Cable companies have approximately 200 video channels that are running 24/7 to their destination receivers, so there is not a lot of joining and pruning happening. There are a few exceptions like local advertising that gets mixed in, but the main channels are up all the time. If no last hop (leaf) routers are pruning any multicast groups, then the prune timers do not count down, and the dense mode flood does not occur. If one or more groups do prune the state refresh option is also available to keep the prune timers from counting to zero which would cause flooding.
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Let me be clear, "I am not advocating dense mode as a solution for most of you out there. I still think sparse mode is a much better choice even for the Cable TV applications, but after arguing with their IT professionals on this issue it is hard not to see their point. In their environment dense mode works and if it isn't broke then why fix it.
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Anyone with a different opinion or would just like to add to the discussion please do so.
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Bill Treneer,
President ICM
Global Knowledge Course Director: Multicasting
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| Last Updated on Wednesday, 26 November 2008 10:20 |