3com S7906E Instruccion De Instalación

 

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To facilitate description, a network comprising IPv6 PIM–supporting routers is referred to as an “IPv6 

PIM domain” in this document. 

 

IPv6 PIM-DM is a type of dense mode IPv6 multicast protocol. It uses the “push mode” for IPv6 

multicast forwarding, and is suitable for small-sized networks with densely distributed IPv6 multicast 

members. 

The basic implementation of IPv6 PIM-DM is as follows:  

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IPv6 PIM-DM assumes that at least one IPv6 multicast group member exists on each subnet of a 

network, and therefore IPv6 multicast data is flooded to all nodes on the network. Then, branches 

without IPv6 multicast forwarding are pruned from the forwarding tree, leaving only those branches 

that contain receivers. This “flood and prune” process takes place periodically, that is, pruned 

branches resume IPv6 multicast forwarding when the pruned state times out and then data is 

re-flooded down these branches, and then are pruned again.  

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When a new receiver on a previously pruned branch joins an IPv6 multicast group, to reduce the 

join latency, IPv6 PIM-DM uses the graft mechanism to resume IPv6 multicast data forwarding to 

that branch.  

Generally speaking, the IPv6 multicast forwarding path is a source tree, namely a forwarding tree with 

the IPv6 multicast source as its “root” and IPv6 multicast group members as its “leaves”. Because the 

source tree is the shortest path from the IPv6 multicast source to the receivers, it is also called shortest 

path tree (SPT).  

The working mechanism of IPv6 PIM-DM is summarized as follows:  

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Neighbor discovery 

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SPT establishment 

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Graft 

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Assert 

In an IPv6 PIM domain, a PIM router discovers IPv6 PIM neighbors, maintains IPv6 PIM neighboring 

relationships with other routers, and builds and maintains SPTs by periodically multicasting IPv6 PIM 

hello messages (hereinafter referred to as “hello messages”) to all other IPv6 PIM routers.  

 

Every IPv6 PIM enabled interface on a router sends hello messages periodically, and thus learns the 

IPv6 PIM neighboring information pertinent to the interface.