R4 is directly connected to both RPs (R2 and R3) R4 is currently sending all ,o,ns upstream to R3 but you want all joins to go to R2 instead Referring to the exhibit, which configuration change will solve this issue?
A.
Change the bootstrap priority on R2 to be higher than R3
B.
Change the default route in inet.2 on R4 from R3 as the next hop to R2
C.
Change the local address on R2 to be higher than R3.
D.
Change the group-range to be more specific on R2 than R3.
The issue arises because R3’s group-range (224.1.1.0/28) is more specific than R2’s group-range (224.1.1.0/24). In PIM bootstrap (BSR), the RP with the longest prefix (most specific group-range) is preferred, regardless of priority. Even though R3 has a higher bootstrap priority (210 vs. R2’s 200), its more specific /28 group-range takes precedence for groups within 224.1.1.0/28.
Why Option D is Correct:
To force R4 to use R2 for all joins, R2’s group-range must be more specific than R3’s. For example:
If R2’s group-range is changed to 224.1.1.0/28 (same as R3) but with a higher priority, R2 would win (priority is compared only when group-ranges are equal).
If R2’s group-range is changed to 224.1.1.0/29 (more specific than /28), it will override R3’s /28 for groups in the /29 range.
The key is prefix specificity, which overrides priority in BSR elections.
Why Other Options Are Incorrect:
A. Change bootstrap priority on R2 to be higher than R3:
Priority is evaluated only when group-ranges are identical. Since R3’s group-range (/28) is more specific than R2’s (/24), R3 will still win for groups in 224.1.1.0/28, even if R2’s priority is higher.
B. Change the default route in inet.2 on R4:
RPF routes (inet.2) determine how traffic reaches the RP, but they do not influence RP election logic (BSR priority/group-range).
C. Change R2’s local address to be higher than R3’s:
The RP address is a tiebreaker only if priorities and group-ranges are equal. Since R3’s group-range is more specific, this change has no impact.
Key Takeaways:
BSR RP Election Order:
Longest group prefix (most specific).
Highest priority (if prefixes are equal).
Highest RP address (if prefixes and priorities are equal).
To override R3, R2 must advertise a more specific group-range (e.g., /28 or smaller) to ensure it is selected for the desired multicast groups.
[Reference:Juniper PIM Sparse Mode and BSR Configuration., , ]
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