Posts Tagged ‘PIM-SM shared-tree’

Basic Multicast part 2 – PIM Sparse Mode – Static RP

August 5, 2012 4 comments

This is the second part of my previous topic about Multicast. This time I will demonstrate how PIM Sparse Mode works based on the same topology as the previous post.

Let´s consider the following topology:

Source: The multicast source will be sending to multicast group which is part of the administratively scoped addresses assigned by IANA which is for use in private multicast domains, much like the IP unicast range defined in RFC 1918.

 RP: The RP is R4 with IP:

 IGP: The IGP used is EIGRP

 Platform/IOS: Cisco 2691/12.4(15)T11 Adv IP services

 As PIM Sparse Mode is a much wider topic than PIM Dense Mode I will start to talk about PIM Sparse Mode with static RP, than Auto-RP, Auto-RP listener and finally PIM BSR.

PIM Sparse Mode is based on the “pull model” or “explicit join” which use a combination of both a shared tree and a source-based tree. The RP is making the connection between the shared-tree (tree build down the Multicast receivers) and the source-based tree (tree built up to the source).

PIM Sparse Mode uses (*,G) entries to forward Multicast traffic unlike PIM Dense Mode. So the key difference between PIM Sparse Mode and PIM Dense Mode is that PIM Sparse Mode the forwarding state in the router is set up as a result of an explicit “join” where in PIM DM (PIM Dense Mode) the forwarding state is set up upon arrival of multicast traffic.

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