300-420 · Question #216
An engineer is designing a PIM Anycast RP solution between two data centers. The design must ensure that RP1 in DC1 and RP2 in DC2 inform each other about specific sources that have joined locally…
The correct answer is B. Enable MSDP between RPs using separate unique loopback interfaces. For a PIM Anycast RP solution across two data centers, RPs must inform each other about local sources; this is achieved by enabling MSDP between them using separate unique loopback interfaces.
Question
An engineer is designing a PIM Anycast RP solution between two data centers. The design must ensure that RP1 in DC1 and RP2 in DC2 inform each other about specific sources that have joined locally. Which solution must the engineer choose?
Options
- AProvision the RPs on the same IP subnet and extend the subnet at Layer 2 between data centers
- BEnable MSDP between RPs using separate unique loopback interfaces
- CEnable MSDP between RPs using the configured Anycast RP address
- DNo action is required because PIM registers from the source will, by default, reach each RP
How the community answered
(29 responses)- A10% (3)
- B79% (23)
- C3% (1)
- D7% (2)
Why each option
For a PIM Anycast RP solution across two data centers, RPs must inform each other about local sources; this is achieved by enabling MSDP between them using separate unique loopback interfaces.
Extending a Layer 2 subnet between data centers for PIM RPs is not the standard or scalable method to share active source information; MSDP is the designated protocol for this purpose.
Multicast Source Discovery Protocol (MSDP) is specifically designed to exchange active source information between different PIM domains or RPs in an Anycast RP setup. Using unique loopback interfaces for MSDP peering provides stable and independent session establishment between RPs, ensuring reliable source advertisement across data centers.
While MSDP is used, peering it directly on the shared Anycast RP address can cause issues as multiple RPs would attempt to source MSDP sessions from the same IP, which is not how MSDP typically establishes unique peer sessions.
PIM register messages are local to the RP receiving them and do not, by default, propagate source information to other RPs across different PIM domains without a mechanism like MSDP.
Concept tested: PIM Anycast RP source information sharing with MSDP
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti/configuration/15-s/imc-15-s-book/imc-anycast-rp.html
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