IP Multicast Routing

[ITexpert]

Hello Guys,

I am kind of confuse or may not understanding it 100 %.

I know what is multicasting and why we need that.  But confuse bw the difference among sparse, dense and sparse-dense mode.

Also explain some scenario when we need one of the mode and why we need that only ?

Thanks

[Jon Marshall]

There are quite a few differences but to put it simply dense mode assumes you want the multicast stream whether you have asked for it or not and it is up to you to say that you don't actually want to receive it. 

Sparse mode only sends the multicast stream when there has been a request for the stream. 

Obviously there is a lot more in terms of implementation details etc. but dense mode is only really suitable for a LAN environment because it can be wasteful of bandwidth although even on LANs you find many people running sparse mode. 

Jon

[ITexpert]

@Jon Marshall  Also what about sparse-dense mode ?  In which scenario Network Engineer will utilize that ?

[balaji.bandi · Accepted solution]

From my notes :

• Dense mode: we forward multicast traffic on all interfaces until a downstream router requests us to stop forwarding.
• Sparse mode: we don’t forward multicast traffic on any interface until a downstream router requests us to forward it.
• sparse-dense mode : where we can use sparse or dense mode for each multicast group, sparse-dense mode also allows us to flood the auto RP 224.0.1.39 and 224.0.1.40 multicast groups but in addition, it also floods all multicast traffic that we don’t have an RP.

Sparse-dense mode, as the name implies, allows the interface to operate on a per-group basis in either sparse or dense mode. A group specified as dense is not mapped to an RP. Instead, data packets destined for that group are forwarded by means of PIM dense-mode rules. A group specified as sparse is mapped to an RP, and data packets are forwarded by means of PIM sparse-mode rules.