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352-001 · Question #179

What is the most efficient method of implementing IP multicast in a network without using RPs?

The correct answer is C. Implement source-specific multicast and utilize the functionality of IGMPv3 to replace the RPs.. Source-Specific Multicast (SSM) eliminates the need for RPs by having receivers specify both the group and the source, and this requires IGMPv3 for its source-filtering capability.

Designing Network Services

Question

What is the most efficient method of implementing IP multicast in a network without using RPs?

Options

  • AImplement PIM dense mode multicast to eliminate the need for RPs.
  • BImplement source-specific multicast and utilize the functionality of IGMPv2 to replace the RPs.
  • CImplement source-specific multicast and utilize the functionality of IGMPv3 to replace the RPs.
  • DRPs can't be eliminated; they're mandatory in multicast networks.

How the community answered

(53 responses)
  • A
    11% (6)
  • B
    4% (2)
  • C
    77% (41)
  • D
    8% (4)

Why each option

Source-Specific Multicast (SSM) eliminates the need for RPs by having receivers specify both the group and the source, and this requires IGMPv3 for its source-filtering capability.

AImplement PIM dense mode multicast to eliminate the need for RPs.

PIM Dense Mode uses flood-and-prune behavior and is inefficient for large networks; while it does not use RPs, it is not the most efficient method for eliminating them.

BImplement source-specific multicast and utilize the functionality of IGMPv2 to replace the RPs.

IGMPv2 does not support source-specific filtering and only allows hosts to join or leave a multicast group without specifying a source, making SSM - which requires source awareness - impossible with IGMPv2.

CImplement source-specific multicast and utilize the functionality of IGMPv3 to replace the RPs.Correct

SSM operates in the 232.0.0.0/8 range and builds shortest-path trees directly from receiver to source without requiring a Rendezvous Point. IGMPv3 is required because it adds source-specific membership reports (INCLUDE/EXCLUDE modes), allowing hosts to specify the exact source address - this is the mechanism that makes RP-free multicast possible and efficient.

DRPs can't be eliminated; they're mandatory in multicast networks.

RPs are not mandatory in multicast networks; SSM is a well-established mechanism specifically designed to operate without RPs, as defined in RFC 4607.

Concept tested: Source-Specific Multicast and IGMPv3 RP elimination

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_pim/configuration/xe-16/imc-pim-xe-16-book/imc-ssm.html

Topics

#source-specific multicast#IGMPv3#PIM SSM#RP elimination

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