Multicasting on a Campus LAN - Dense or Sparse...

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May 22nd, 2009
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Hi All,

I am currently looking into multicast network and have a question on the best practice recommendations for PIM Sparse mode and PIM dense mode.

I am familiar with how both protocols operate and what is necessary to get them going, but i just want to know if there is an "obvious" best one to use in my situation.

Basically, we want to setup Ghost to allow PC images to be multicast over the network. the Server will sit in the Server VLAN, clients will sit in various VLANs across the site. All of the switches are connected back to the core via 1Gbps fibre backbones and there is the potential to expand this to another 2 sites which are connected with 100Mbps LES circuits.(I think i will push for local ghost servers for those sites..)

So, which is the most efficient Multicast routing protocol to operate in this situation. The reseacrh i have done so far see's people favouring PIM Sparse-Dense mode, which makes sense - but do i do this AND configure an RP for the ghost traffic? If so, why do i not simply use PIM sparse mode? And vica versa - if i enable PIM Sparse-Dense mode and do not configure an RP, does it simply revert to dense mode operation?

Any thoughts and advice much appreciated,



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Jon Marshall Fri, 05/22/2009 - 07:10
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The most efficient really depends on how many clients will need to receive the stream at any one time. Personally i would use sparse mode in your scenario, saves on Ghost traffic being flooded then pruned on vlans that have no clients.

If you statically configure the RP on all your L3 devices then you don't need auto-rp and consequently you don't need pim sparse-dense mode ie. you can just use pim sparse mode.

If you do want to use auto-rp then you still don't actually have to use pim sparse-dense mode you can just use pim sparse mode and use the "ip pim autorp listener" global command.


jonathanaxford Tue, 05/26/2009 - 23:48
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Hi Jon,

Thanks for the info. I was leaning towards sparse mode, mainly due to the fact we will only be ghosting machines on one or two VLANs. Statically assigning an RP sounds like the best way forward for me too, the network is not huge and to begin with, most of the multicast will revolve around the same core switch.

Thanks again,



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