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Multicast and shared tree, router distribution

"In a shared tree, the root of the distribution tree is a router, not a host, and located somewhere in the core of the network".,,,,please pay attention to phrase: "not a host".

The same quote above is found in the below book , but without phrase: "not a host".

Another article :

"Unlike source trees that have their root at the source, shared trees use a single common root placed at some chosen point in the network. This shared root is called the rendezvous point (RP)".

Since the above articles are related to shared tree,I concluded (any comment) that source tree (as comparison) have :

1- A host (not a router) as a source of multicast.

2- This host is root of the tree as well.

But again my conculsion is contradicted with the below article:

"------Each tree is rooted at a router adjacent to the source-----"

Any clarification



Re: Multicast and shared tree, router distribution

first part incorrect,

a source-based can be a router or a host.

second part correct,

this host or router will be the root, of the source-based distribution tree.

when your host registers with an RP, the RP sends a join toward the source. this is called using a 'shared-source distribution tree'. (the RP is the root)

if a specific source is required/usuable, then the hosts first hop router may send a join toward the source to create a 'source-based distribution tree'. (a source-based distribution tree does not require the use of the RP for tracking the group membership of the host using it; a shared-source distribution tree does)

see these links for more MCast info:

Cisco Employee

Re: Multicast and shared tree, router distribution

- The root of a shared tree is a router (RP).

- The root of a source tree is a any device that can be the source of multicast feed.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
México móvil: +52 1 55 8312 4915
Cisco México
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Ciudad de México, 06600
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