Why cannot a multicast distribution tree be set up correctly if PIM is not enabled on an RPF interface


The PIM protocol does not maintain its own unicast routing table. Instead, it uses the existing unicast routing table for RPF checks. Generally, the object of an RPF check is the multicast source. On a PIM-SM network, the object of an RPF check can be the multicast source, RP, or BSR. A PIM device searches the unicast routing table for an optimal route to an object. The outbound interface of the route is an RPF interface. That is, whether an interface is an RPF interface depends on unicast routing and is independent of the PIM protocol. The PIM protocol requires that PIM be enabled on an RPF interface. If PIM is not enabled, the RPF interface cannot process received PIM protocol packets, and therefore the multicast distribution tree cannot be set up.

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Why cannot an Up interface be selected as the working interface
The reason is that this interface works in half duplex mode. On a switch, if the rate of an interface is the same as that of member interfaces in an Eth-Trunk, this interface can be added to the Eth-Trunk. However, if this interface works in half duplex mode, the Eth-Trunk will not select it as the working interface.

On which interfaces does PIM need to be enabled
When receiving a multicast packet, a switch performs Reverse Path Forwarding (RPF) check on the packet and searches for the optimal route to the destination. The outbound interface of the route is the RPF interface and the next hop of the route is the RPF neighbor. A multicast forwarding entry can be created only after PIM is enabled on the RPF interface and the RPF neighbor. In this way, a complete multicast distribution tree can be set up along the forwarding path of the packet. It is recommended that you enable PIM on all non-edge interfaces in the PIM domain because all these interfaces have a chance to become an RPF interface or RPF neighbor. On the switch directly connecting to a multicast source, the RPF interface for packets sent from the multicast source is the interface connected to the multicast source. Therefore, PIM must be enabled on this interface.

Can a PIM domain run PIM-DM and PIM-SM simultaneously
A PIM Domain cannot run PIM-DM and PIM-SM simultaneously. Since PIM Hello packets do not carry messages in PIM mode, a PIM switch cannot know the mode of the PIM protocol that its PIM neighbor runs. If the RPF interface and the RPF neighbor run PIM protocols of different modes, two neighboring devices cannot learn PIM routing information from each other. As a result, related multicast forwarding entries cannot be correctly created.

Why Topologies Cannot Be Displayed Correctly on Chrome?
Open Chrome. In the address box, enter chrome://plugins/ to go to the plug-in management interface. Click Details to view details about the plug-in of Chrome. View details about Adobe Flash Player. Stop plug-ins except for official plug-ins in the installation directory of Chrome. Log in to OceanStor ReplicationDirector using Chrome again.

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