Pim Dm - TP-Link T3700G-28TQ User Manual

2 Enable IGMP on
user-side
interface.
Configure Switch C

Steps Operation
1 Enable IP
multicast routing.
2 Enable IGMP on
user-side
interface.

11.3 PIM DM

In this section we firstly outline PIM protocol, RPF Check mechanism and the two modes of PIM,
then introduce the working process of PIM DM.
PIM is a popular multicast routing protocol within the AS. Instead of relying on one specific
unicast routing protocol, PIM uses the static routing or unicast routing table generated by any
unicast routing protocol (including RIP, OSPF, IS-IS, BGP etc.) to perform routing for IP multicast
data.
Unlike some other multicast routing protocols, PIM doesn't update routing information between
routers or maintain an independent route forwarding table. PIM uses the RPF (Reverse Path
Forwarding) check mechanism to forward the multicast data.
There are two types of multicast routing and forwarding tables in the multicast implementation:
All the multicast route information will be summarized as a general multicast routing-table;

The multicast forwarding-table is used to control the forwarding of the multicast packets

directly.
The multicast routing table consists of a group of (S, G) entries, and (S, G) route represents
routing information from source S to group G. If the router supports multiple multicast routing
protocols, its multicast routing table will contain multicast routes generated from multiple
protocols. The router will chose the optimal multicast route according to multicast routing and
forwarding strategy, and send it to the multicast forwarding table.
The multicast routing protocol uses the RPF mechanism to establish the multicast routing
entries, thus to guarantee the multicast data being transferred in the correct path.
RPF Mechanism

PIM uses the unicast routing table to perform the RPF check. RPF mechanism ensures the
multicast packets being forwarded correctly according to the multicast routing configuration,
and avoids loops causing by various reasons.
On page Multicast Routing→ IGMP→ Interface Config, enable
IGMP (version 2) on interface VLAN 20.
Note
On page Multicast Routing→ Global Config→ Global Config,
enable the multicast routing function.
On page Multicast Routing→ IGMP→ Interface Config, enable
IGMP (version 2) on interface VLAN 20.
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