The PIM protocol is used to implement multicast routing
and data forwarding inside an AS. The PIM-SM protocol is a multicast
routing protocol of sparse node. It is applicable to a large-scale
network with sparsely-distributed members.
The key mechanisms of PIM-SM are neighbor discovery, Designated router (DR) election, assert, Rendezvous Point (RP) discovery, join, register, shortest path tree (SPT) switchover, and prune.
This section describes the multicast data forwarding process in a PIM-SM domain, PIM control message types, PIM reliability, and security functions required for the multicast service.
Ensure that unicast routes are reachable before configuring IPv4 multicast routing and enable PIM-SM on each interface of the multicast device. Configure static or dynamic Rendezvous Point (RP) so that the PIM-SM network can work normally.
A multicast device can control the forwarding of multicast data based on multicast sources. This helps to control multicast data flows and limit information that can be obtained by downstream receivers to enhance security.
If a dynamic Rendezvous Point (RP) is used, you can adjust parameters of Candidate-RPs (C-RPs) and Candidate-BSRs (C-BSRs) as required. If there is no special requirement, default values are recommended.
A PIM-SM network can be divided into multiple bootstrap router (BSR) administrative domains and a global domain. This effectively reduces the load of a single BSR, and provides a special service for specific multicast groups.
Multicast devices establish PIM neighbor relationships and negotiate various control parameters by exchanging Hello messages. You can adjust the parameters carried in Hello messages as required. If there is no special requirement, adopt default values.
In a PIM-SM network, the DR directly connected to the multicast source encapsulates multicast data in a Register message and sends it to the Rendezvous Point (RP) in unicast mode. The RP then decapsulates the message, and forwards the multicast data to receivers along the rendezvous point tree (RPT). The system supports the Register message filtering and suppression functions.
A multicast device sends Join messages upstream to require to forward multicast data and Prune messages upstream for requiring to stop forwarding multicast data. You can adjust control parameters for multicast data forwarding as required. If there is no special requirement, adopt default values.
If a multicast device can receive multicast data through the downstream interface, this indicates that other upstream devices exist in this network segment. The device then sends an Assert message through the downstream interface to take part in the election of the unique upstream device.
A high volume of multicast data traffic increases the load of a Rendezvous Point (RP), and may result in a fault. To solve this problem, PIM-SM allows the RP or the DR at the group member side to trigger the shortest path tree (SPT) switchover when the rate of multicast packets is high.
The interface directly connecting a multicast device to a user host needs to be enabled with PIM. In this case, some malicious hosts may simulate a large number of PIM Hello messages and send the messages to the interface for processing. As a result, the multicast device is suspended. To avoid the preceding case, you can set the interface to be in the PIM Silent state.
When the NAT device divides the intranet and extranet into two independent multicast domains, you can configure the multicast NAT function to enable intranet receivers to access extranet resources.
You can use related commands to display the PIM-SM running status. If necessary, you can clear the PIM-SM control message statistics or enable the PIM-SM debugging.