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New Member

Multicast PIM Dense and Sparse Mode_DR Router

Hi All,

I have a great confusion between PIM Dense and Sparse Mode.


In PIM Dense Mode do they have the Concept of DR router?

If so, DR router functions same for both dense and sparse mode i,e to forward the PIM join request?

Can some give a detailed explanation between dense and sparse mode?

Thanks in advance!!





Cisco Employee

Nivetha,A simple way to


A simple way to understand is:

Dense Mode== No DR concept( Dense means you would send it to all the routers)

Sparse Mode == DR concept is there.


Let me go in details:-


PIM Dense mode:


PIM Dense mode is more similar to Source tree. In dense mode Source Tree will be start from source of network who is generating multicast traffic and other Multicast host Routers will be acting as branches of Tree which are trying to access the multicast stream. In PIM dense mode Router will initially flood multicast packet across network. This process will help in creation of (S, G) entry in all routers. This process is repeated every three minutes in PIM dense mode.  In this process those routers which don’t need the multicast stream that router will prune back the traffic flow.

PIM Dense mode is also known as PUSH MODE.
PIM dense is recommended for small networks.
PIM dense mode is very easy to configure on Routers.
PIM dense mode is not scalable.


For summary – PIM dense mode is flooded across the network, then Routers which don’t have request for that particular group will prune it. The PIM dense tree is formed. Same process is repeated every three minutes. This process is not efficient in large enterprises network. So PIM dense mode is used in small networks, to avoid more configurations and easy management.


PIM Sparse mode similar to shared Tree. PIM sparse mode is having a central point of contact for all Multicast host routers. As the Routers will receive the request from host to join particular multicast group, They will check the multicast routing table which is received from PIM and in case of the router is not aware, The request will be forwarded to RP (Rendezvous Point). RP is a designated router in network selected by network administrator as per requirement/Topology. This router will be responsible for providing information about every multicast group to host. All multicast source will register with RP. RP will aware about all multicast group and how to reach to multicast source.

                As RP will receive request from host, It will update source information and path to host router. Same time host router will use IGP information and find the best path and reach to source.

                In sparse mode, RP plays very important role. We can configure RP in many ways. For Cisco routers we can configure Auto-RP, other way are Static RP in each router and BSR – Industry standard (bootstrap router). 

Now we need to understand. In sparse mode RP is playing major role. You can designate a Central Router as RP and every Multicast host traffic will pass thru RP.

Some key point of PIM Sparse Mode - 

Sparse mode is recommended for structured Multicast network Design
We can say, it is very useful in large networks. We can deploy redundant RP to manage our network efficiently.
Sparse mode requires planning for deployment. It is having some more configurations as compared to dense mode.
PIM sparse mode is pull mode.
Sparse mode is scalable.

Sparse mode command –
Interface mode – ip pim sparse-mode

                                             I explained in very simple language, which will clear your concepts about PIM and PIM Dense mode and PIM Sparse mode easily.

Hope this information is useful to you..



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New Member

Insharie,Thanks for the reply


Thanks for the reply and it was really helpful.

I have few more doubts regarding Dense and Sparse Mode

In Dense Mode-a IGMP request , PIM join request will be send?

In Dense Mode when a host leaves a particular Multicast address will there be any IGMP leave message?

For Dense Mode do we have to enable IGMP Snooping on switches?




Hello Nivetha01In Dense Mode

Hello Nivetha01

In Dense Mode-a IGMP request , PIM join request will be send?

- No there is no PIM join request in Dense Mode, why because PIM DM would assume that all the devices in the domain require multicast stream and flood the traffic

In Dense Mode when a host leaves a particular Multicast address will there be any IGMP leave message?

-If there is IGMP V2 enabled on an interface, irrespective of Dense/Sparse mode, The host  sends leave message. If we are using dense mode of operation, the multicast traffic will be flooded every 3 minutes and the routers with no client associated will prune back the unwanted traffic

For Dense Mode do we have to enable IGMP Snooping on switches?

- IGMP snooping is an enhancement to make the multicast switching in the layer2 domain. So again whether it is Dense/Sparse, it is good to have feature on the switches to reduce the unwanted flooding


Hope this helps







New Member

Harish,Thanks a lot for the


Thanks a lot for the reply.

New Member

Hi,Can anyone let me know


Can anyone let me know what kind of interview questions will be asked for multicast?

Thanks in advance!!



Cisco Employee

Nivetha01,Its all depends on


Its all depends on the interviewer.

Below are some threads discussing the same:

Here is my suggestion:


1- Have clear understanding what multicast is?

2- Modes of multicast/.

3- Difference between Igmp version( v1,v2,v3)

4- Brief overview of RP,auto-rp and BSR.

Once you are through with this you should be able to handle any questions.


********Please dont forget to rate this post if this is helpfull.

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