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Table of Contents
In this lesson, we will learn a multicast routing protocol, PIM (Protocol Independent Multicast). If we answer the first question, what is PIM, PIM is basically a routing protocol used for multicast routing. By using PIM, the multicast traffic is routed to its destination, reaches multicast clients.
You can also check IGMP and IGMP Snooping lessons.
PIM is independent from the IGP (Interior Gateway Protocol). You can be using OSPF, EIGRP, IS-IS or any other routing protocols inside your network. PIM do not care about it. It only needs IGP convergence and routing table of IGP. PIM do not need its own routing table.
For multicast routing, PIM creates Multicast Tree and multicast traffic goes through this Multicast Path. Unlike PIM, other multicast routing protocols like DVMRP and MOSPF creates their own routing table for multicast routing.
As a routing protocol, PIM differentiates from the other routing protocols. Other routing protocols send and receive routing updates. But PIM does not send and receive routing updates.
PIM (Protocol Independent Multicast) does not build an independent complete multicast routing table. Instead of this, PIM uses a unicast routing table for RPF (Reverse Path Forwarding Check). We will talk about what is RPF in another lesson.
You can test your IP Multicast Knowledge with Multicast Questions!
Protocol Independent Multicast uses different modes. In other words, it has different types. There are four different modes used with this protocol. These PIM modes are given below:
PIM-DM (PIM Dense Mode) is the PIM mode which uses push model. In this model, at the beginning, the source router floods the multicast traffic to all the recipients even if they are not related in that multicast traffic. After this flood, the uninterested nodes send prune requests that means they do not want to receive this multicast traffic. With these prune messages, uninterested and interested nodes are detected. After that, the multicast traffic is sent though the ports towards the interested recipients. Other ports are pruned. The other name of this multicast model is flood and prune.
PIM-SM (PIM Sparse Mode) is the PIM mode which uses a pull model. In this model, the multicast traffic is sent only to the multicast receivers that request this multicast traffic. In other words, only interested nodes received multicast traffic. PIM-SM uses Randevous-Point (RP). Randevous Point is a meeting point of multicast source and multicast receivers. With the use of RP, the multicast traffic is not flooded like PIM-DM, but the receivers which send join requests, are added to the Multicast Tree. This is on demand multicast routing.
(PIM Sparse Dense Mode) is a PIM mode which uses both PIM Dense mode and PIM Sparse mode in group basis. In this mode the group works with dense mode, uses dense mode rules and it is not mapped to the Randevous-Point (RP). On the other hand, the group works with sparse mode, uses sparse mode rules and it is mapped to RP. It works with the rules of sparse mode.
PIM-SSM (Souce Specific Multicast) is a PIM-SM based enhanced PIM method. It is used with IGMPv3. With PIM-SSM, receivers can receive multicast traffic from a specific multicast source. In Source Specific Multicast, source discovery responsibility shifts from multicast network to multicast receiver.
Bidirectional PIM is an enhancement to Protocol Independent Multicast. With this enhancement an efficient communication is provided in PIM domain. Only shared trees are used with Bidirectional PIM and the receivers can also start the communication towards the randevous-point. Bidirectional PIM mechanism decreases the used resources on other PIM modes.
In this lesson, we have learned what is PIM (Protocol Independent Multicast) and why we use this multicast routing protocol briefly. We have also talked about four types of this multicast routing protocol. We have learned dense mode, sparse mode, sparse-dense mode and bidirectional-pim briefly. For different networks, you can use these modes according to your networks need. In the following lessons, we will learn the details of these PIM modes. We will also learn the configuration of these modes one by one.
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