352-001 · Question #649
When designing a Source Specific Multicast solution, what must you consider?
The correct answer is C. The IANA assigned range is 232.0.0.0/8. Source Specific Multicast (SSM) uses the IANA-reserved 232.0.0.0/8 range and eliminates Rendezvous Points by allowing receivers to subscribe directly to a specific source.
Question
When designing a Source Specific Multicast solution, what must you consider?
Options
- AIt lacks support for URL Rendezvous Directory
- BInitial multicast traffic will flow over the RPT
- CThe IANA assigned range is 232.0.0.0/8
- DEmbedded RP can be used for RP discovery
How the community answered
(22 responses)- A5% (1)
- B5% (1)
- C91% (20)
Why each option
Source Specific Multicast (SSM) uses the IANA-reserved 232.0.0.0/8 range and eliminates Rendezvous Points by allowing receivers to subscribe directly to a specific source.
URL Rendezvous Directory (URD) is a Cisco mechanism specifically designed to aid SSM source discovery, meaning SSM does have support for URD rather than lacking it.
SSM does not use a Rendezvous Point Tree (RPT) at all - traffic always flows directly on the Shortest Path Tree from source to receiver; initial RPT usage is a characteristic of PIM-SM Any Source Multicast, not SSM.
IANA has officially reserved the 232.0.0.0/8 address block exclusively for SSM. Multicast groups within this range use IGMPv3 (S,G) joins so receivers specify both the source and the group address, and traffic always flows on the Shortest Path Tree directly from the source with no RP involved.
Embedded RP is a PIM-SM feature used in IPv6 ASM deployments to encode the RP address within the group address for RP discovery; SSM has no RP and therefore embedded RP is not applicable.
Concept tested: SSM IANA address range and RP-less multicast design
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_ssm/configuration/xe-16/imc-ssm-xe-16-book/imc-ssm.html
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