Discuss Juniper JN0-664 Exam Topic 10 Question 34

Which two statements are correct regarding the PIM DR in a PIM-SM domain? (Choose two.)

AThe source DR sends PIM register messages from the source network to the RP.

BIf the DR priorities match, the router with the lowest IP address is selected as the DR.

CThe receiver DR sends PIM join and PIM prune messages from the receiver network toward the RP.

DBy default, PIM DR election is performed on point-to-point links.

Suggested Answer: A, C

In PIM-SM (Protocol Independent Multicast - Sparse Mode), the Designated Router (DR) plays a crucial role in multicast forwarding. The DR is responsible for various tasks depending on whether it is connected to the source or the receiver. Let's analyze each statement regarding the PIM DR in a PIM-SM domain.

1. **Statement A: The source DR sends PIM register messages from the source network to the RP.**

- Correct. In PIM-SM, the DR on the source's local network is responsible for encapsulating multicast packets in PIM Register messages and sending them to the Rendezvous Point (RP). This process ensures that the RP is aware of active sources.

2. **Statement B: If the DR priorities match, the router with the lowest IP address is selected as the DR.**

- Incorrect. The correct rule is that if the DR priorities match, the router with the **highest** IP address is selected as the DR. The election process first compares priorities; if priorities are equal, the IP addresses are compared to select the DR.

3. **Statement C: The receiver DR sends PIM join and PIM prune messages from the receiver network toward the RP.**

- Correct. In PIM-SM, the DR on the receiver's local network sends PIM Join messages toward the RP to join the multicast distribution tree. Similarly, it sends PIM Prune messages to leave the tree when there are no interested receivers.

4. **Statement D: By default, PIM DR election is performed on point-to-point links.**

- Incorrect. By default, PIM DR election is performed on multi-access networks (e.g., Ethernet). On point-to-point links, there is no need for a DR election as there are only two routers involved.

**Conclusion**:

The correct statements regarding the PIM DR in a PIM-SM domain are:

**A. The source DR sends PIM register messages from the source network to the RP.**

**C. The receiver DR sends PIM join and PIM prune messages from the receiver network toward the RP.**

**Reference**:

- Juniper Networks Documentation on PIM-SM: [PIM-SM Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/pim-sparse-mode-overview.html)

- RFC 7761, Protocol Independent Multicast - Sparse Mode (PIM-SM): [RFC 7761](https://tools.ietf.org/html/rfc7761) which details the PIM-SM protocol, including DR roles and election procedures.

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31 comments · newest first

Tonette 11 months ago

I don't know, C sounds off to me.

Craig 11 months ago

Wait, DR election on point-to-point links? Really?

Stefania 11 months ago

Definitely A and D!

Whitney 11 months ago

I think B is right too, but not sure about A.

Germaine 12 months ago

A and C are correct!

Thora 12 months ago

I practiced a similar question about PIM DR elections, and I believe that by default, they do happen on point-to-point links, but I need to double-check that.

Ezekiel 1 year ago

I’m a bit confused about the receiver DR sending join and prune messages. I thought that was the role of the source DR?

Letha 1 year ago

I remember something about DR priorities, and I think if they match, the router with the lowest IP address does get selected. That sounds familiar.

Stephanie 1 year ago

I think the statement about the source DR sending PIM register messages is correct, but I'm not entirely sure about the details of the DR election process.

Mose 1 year ago

I'm a bit confused about the differences between the source DR and the receiver DR. I think option A is correct, but I'm not 100% sure about the other options. I'll select A and hope for the best on the second one.

Moon 1 year ago

Okay, I remember from the lectures that the PIM DR election is based on the router priority, and if those match, the lowest IP address is selected. So I'll go with option B. The other options are a bit unclear to me, so I'll have to skip those.

Claudio 1 year ago

Hmm, this question is a bit tricky. I'm not entirely sure about the PIM DR responsibilities, but I think option C sounds right - the receiver DR sends the join and prune messages. I'll select that one and take an educated guess on the other.

Noemi 1 year ago

I'm pretty sure the PIM DR is responsible for sending the PIM register messages, so I'll select option A. The other options seem a bit trickier, but I'll try to reason through them.

Leontine 1 year ago

I've got this! The NEW state means the application hasn't been accessed yet, so option A is the correct answer. The server's state doesn't matter in this case.

Kiley 2 years ago

I'm with Lawrence on this one. A, C, and D seem like the way to go. PIM can be a real headache sometimes, but at least it keeps us on our toes!

Lawrence 2 years ago

Hmm, this question is a real brain-teaser. I'm going to go with my gut and say A, C, and D. Gotta love these tricky PIM questions!

Denise 2 years ago

↳ replying to Lawrence

User1: Exactly, that's how the PIM DR works in a PIM-SM domain.

Douglass 2 years ago

↳ replying to Lawrence

User2: I agree, the source DR sends PIM register messages and the receiver DR sends PIM join and prune messages.

Felix 2 years ago

↳ replying to Lawrence

User1: I think the correct statements are A and C.

Lazaro 2 years ago

B is also correct. The router with the lowest IP address is selected as the DR when the DR priorities match.

Myra 2 years ago

D is definitely correct. PIM DR election is performed on point-to-point links by default.

Becky 2 years ago

↳ replying to Myra

Yes, D is correct. The DR with the lowest IP address is selected if priorities match.

Aileen 2 years ago

↳ replying to Myra

D) By default, PIM DR election is performed on point-to-point links.

Dortha 2 years ago

↳ replying to Myra

A) The source DR sends PIM register messages from the source network to the RP.

Tamar 2 years ago

I'm not sure about statement A, but I think statement C is correct because the receiver DR sends PIM join and prune messages.

Orville 2 years ago

I think A and C are the correct answers. The DR sends the necessary messages to the RP in a PIM-SM domain.

Micaela 2 years ago

↳ replying to Orville

I agree with you, A and C are the correct statements regarding the PIM DR in a PIM-SM domain.

Kerry 2 years ago

↳ replying to Orville

I think it's actually B and D. The router with the lowest IP address becomes the DR.

Cherilyn 2 years ago

↳ replying to Orville

I believe A and C are correct. The DR sends messages to the RP in a PIM-SM domain.

Ligia 2 years ago

I agree with you, Leonor. I also believe that statement D is correct as PIM DR election is done on point-to-point links by default.

Leonor 2 years ago

I think statement B is correct because the router with the lowest IP address becomes the DR.

Juniper JN0-664 Exam - Topic 10 Question 34 Discussion