Question 81 of 530 from exam 400-251: CCIE Security written exam

Question 81 of 530 from exam 400-251: CCIE Security written exam

Question

Which three statements are true about PIM-SM operations? (Choose three.)

Answers

Explanations

A. B. C. D. E.

ACD.

PIM-SM (Protocol Independent Multicast-Sparse Mode) is a multicast routing protocol that is widely used in enterprise and service provider networks. It provides an efficient way to distribute multicast traffic from a source to a group of receivers, while minimizing the amount of network bandwidth used.

The three statements that are true about PIM-SM operations are:

A. PIM-SM supports RP configuration using static RP, Auto-RP, or BSR. In PIM-SM, the Rendezvous Point (RP) is the root of the multicast distribution tree. PIM-SM supports multiple methods for configuring the RP, including static RP, Auto-RP, and Bootstrap Router (BSR). Static RP is manually configured, while Auto-RP and BSR are automatic methods that use multicast packets to discover the RP.

B. PIM-SM uses a shared tree that is rooted at the multicast source. PIM-SM uses two types of multicast trees: a shared tree and a source-specific tree. The shared tree is rooted at the RP and is used to forward multicast traffic from the source to the receivers. The shared tree is also known as the RPT (Rendezvous Point Tree) or the (*,G) tree, where * represents any source and G represents the multicast group.

C. Different RPs can be configured for different multicast groups to increase RP scalability. PIM-SM supports the configuration of multiple RPs, which can be used for different multicast groups. This increases RP scalability and allows for better load balancing. Each RP is responsible for forwarding multicast traffic for a specific group, and multicast traffic from different groups can be distributed among different RPs.

D. Candidate RPs and RP mapping agents are configured to enable Auto-RP. Auto-RP is a method of automatically discovering RPs in a PIM-SM network. Candidate RPs are multicast-enabled routers that can become an RP, while RP mapping agents are routers that receive and distribute the RP mapping information. To enable Auto-RP, candidate RPs and RP mapping agents need to be configured with the appropriate settings.

E. PIM-SM uses the implicit join model. PIM-SM uses an explicit join model, where receivers explicitly join the multicast group by sending IGMP (Internet Group Management Protocol) messages to their local router. The router then sends PIM join messages upstream towards the RP to establish the multicast distribution tree. The implicit join model is used in PIM-SSM (Source-Specific Multicast), where the receiver specifies both the source and group in the IGMP message.

In summary, PIM-SM is a multicast routing protocol that supports multiple RP configurations, uses a shared tree rooted at the RP, allows for multiple RPs for different multicast groups, can use Auto-RP for RP discovery, and uses an explicit join model for multicast traffic forwarding.