Juniper JN0-664 Exam Dumps

In a PIM Sparse Mode (PIM-SM) domain, Anycast RP is used for load balancing and redundancy by configuring multiple RPs with the same IP address. However, for active multicast sources to be shared between RPs, an additional mechanism is needed since PIM-SM does not automatically synchronize sources between RPs.

Evaluating the Answer Choices

Option A: 'Configure MSDP on each RP router.'

Multicast Source Discovery Protocol (MSDP) is required in an Anycast RP setup to share active source information between RPs.

MSDP allows RPs to exchange source-active (SA) messages, ensuring that multicast receivers in different regions can still receive traffic from sources registered with different RPs.

Juniper Documentation confirms that MSDP is used to synchronize active sources across multiple RPs in an Anycast RP deployment.

This is a correct answer.

Option B: 'Configure anycast PIM with the rp-set statement on each RP router.'

Anycast PIM allows multiple RPs to share the same IP address, and the rp-set statement is used to define the set of Anycast RPs.

This enables receivers and sources to register with the closest RP.

However, Anycast PIM alone does not share active source information between RPs; MSDP is still needed for that.

The combination of Anycast PIM (rp-set) and MSDP is the correct approach.

This is a correct answer.

Option A (Correct):

Complete Sequence Number PDUs (CSNPs)are periodically flooded by theDesignated Intermediate System (DIS)on multi-access networks (e.g., Ethernet).

This ensures all routers on the segment synchronize theirLink-State Databases (LSDBs).

Option C (Correct):

Partial Sequence Number PDUs (PSNPs)containonly the headers (descriptions)of LSPs (e.g., LSP ID, sequence number, checksum).

PSNPs are used to:

Request missing LSPs(when a router detects discrepancies via CSNPs).

Acknowledge LSP receipt(in point-to-point networks).

They donotinclude the full LSP data.

Why Other Options Are Incorrect:

Option B:Incorrect. PSNPs arenot flooded periodically---they are senton-demandfor specific LSP synchronization.

Option D:Incorrect. While CSNPsdocontain LSP descriptions (headers), the term 'only' is misleading. CSNPssummarize all LSPsin the LSDB, but they are not limited to 'only' descriptions---they serve as a complete database overview.

Key Takeaways:

CSNPsareperiodic,broadcastby the DIS, and ensure LSDB consistency.

PSNPsaretriggered, containspecific LSP headers, and handle requests/acknowledgments.

IS-IS usesCSNPs and PSNPsto maintain efficient LSDB synchronization without flooding full LSPs unnecessarily.

For further details, refer to Juniper's official IS-IS documentation: Juniper IS-IS Configuration Guide.

Intermediate System to Intermediate System (IS-IS) is a link-state routing protocol used to move information efficiently within a computer network. It uses a series of Protocol Data Units (PDUs) to manage the network's topology and ensure consistency across all routers in the network. Specifically, Link State PDUs (LSPs), Complete Sequence Number PDUs (CSNPs), and Partial Sequence Number PDUs (PSNPs) play crucial roles in this process.

1. **PSNPs (Partial Sequence Number PDUs)**:

- **Acknowledge a received LSP**: PSNPs are used to acknowledge the receipt of LSPs. When a router receives an LSP, it sends a PSNP back to the sender to confirm that the LSP has been received.

- **Request a missing LSP**: PSNPs are also used to request missing LSPs. If a router identifies a missing LSP based on sequence numbers, it can send a PSNP to request the specific LSP from its neighbors.

2. **CSNPs (Complete Sequence Number PDUs)**:

- **Summarize LSPs**: CSNPs are used to summarize all the LSPs known to a router. They are typically sent at regular intervals to provide a complete list of LSPs in a database. They are not used to acknowledge or request specific LSPs but provide an overview of all LSPs for database synchronization.

Based on this understanding, let's evaluate the statements:

- **A. PSNPs are used to acknowledge a received LSP.**

- Correct. PSNPs serve the purpose of acknowledging LSPs received from other routers.

- **B. CSNPs are used to acknowledge a received LSP.**

- Incorrect. CSNPs are not used for acknowledging LSPs; they are used to provide a summary of all LSPs.

- **C. CSNPs are used to request a missing LSP.**

- Incorrect. CSNPs are not used to request missing LSPs; this is the role of PSNPs.

- **D. PSNPs are used to request a missing LSP.**

- Correct. PSNPs are used to request specific missing LSPs when a router detects that it is missing information.

**Conclusion**:

The correct statements about IS-IS are:

**A. PSNPs are used to acknowledge a received LSP.**

**D. PSNPs are used to request a missing LSP.**

**Reference**:

- Juniper Networks Documentation on IS-IS: [IS-IS Overview](https://www.juniper.net/documentation/en_US/junos/topics/concept/is-is-routing-overview.html)

- RFC 1195, Use of OSI IS-IS for Routing in TCP/IP and Dual Environments: [RFC 1195](https://tools.ietf.org/html/rfc1195) which details the operation and use of IS-IS, including the roles of PSNPs and CSNPs.

Analyzing the Exhibit and Understanding the Issue

The exhibit shows BGP configurations on CE-1 and PE-1, which are connected via EBGP.

CE-1 (Customer Edge)

Uses AS 64511 and establishes an EBGP session with PE-1 (AS 65550).

Configured to export 10 static routes (192.168.1.0/24 - 192.168.10.0/24) using the static-to-bgp policy.

PE-1 (Provider Edge)

Uses AS 65550 and is peering with CE-1 (AS 64511).

Configured with a prefix-limit of 5 on received routes from CE-1.

Teardown enabled, meaning if more than 5 prefixes are received, the BGP session is shut down.

Identifying the Problem

CE-1 is correctly configured with peer AS 65550, so Option B ('CE-1 is configured with an incorrect peer AS') is incorrect .

CE-1 is advertising exactly 10 static routes (as per policy).

PE-1 has a prefix-limit maximum 5 with teardown enabled.

This means that when CE-1 advertises more than 5 prefixes, PE-1 shuts down the BGP session.

BGP moves to the 'Active' state, indicating that the session has been disrupted and PE-1 is trying to re-establish the connection.

CE-1 is reachable since the session was initially established before the limit was exceeded, so Option D ('CE-1 is unreachable') is incorrect .

CE-1 is not advertising its entire routing table, only the static prefixes listed in the policy, so Option A ('CE-1 is advertising its entire routing table') is incorrect .

Correct Answer

C. The prefix limit has been reached on PE-1

Verification from Juniper Documentation

Juniper BGP Prefix Limit Documentation confirms that exceeding the prefix limit with teardown causes the BGP session to go into 'Active' state.

Juniper Troubleshooting Guide for BGP Peering Issues states that when a BGP session reaches the prefix limit and has teardown enabled, the session is terminated.

In IS-IS (Intermediate System to Intermediate System) routing, each router is identified by a unique ISO (International Organization for Standardization) address, also known as a Network Entity Title (NET). The NET consists of three parts:

1. **Area Identifier**: Indicates the area to which the router belongs.

2. **System Identifier**: Uniquely identifies the router within the area.

3. **NSAP Selector (NSEL)**: Typically set to 00 for a router, indicating the Network Service Access Point.

The format of the ISO address is `49.XXXX.YYYY.YYYY.ZZZZ.ZZZZ.00`, where:

- `49` is the AFI (Authority and Format Identifier) indicating a private address.

- `XXXX` is the Area Identifier.

- `YYYY.YYYY.YYYY` is the System Identifier.

- `ZZZZ.ZZZZ` is the NSAP Selector.

Given the address `49.0001.00a0.c96b.c490.00`:

- **Area Identifier**: `49.0001`

- **System Identifier**: `00a0.c96b.c490`

- **NSAP Selector**: `00`

**Explanation**:

- **A. 00a0.c96b.c490 is the system identifier**:

- Correct. The System Identifier in an ISO address is a 48-bit (6-byte) field used to uniquely identify the router. In this address, `00a0.c96b.c490` is the correct 6-byte System Identifier.

- **B. 0001.00a0.c96b.c490 is the system identifier**:

- Incorrect. This includes the Area Identifier as part of the System Identifier, which is not correct.

- **C. c96b.c490 is the system identifier**:

- Incorrect. This is only part of the System Identifier. The full System Identifier must be 6 bytes long.

- **D. c490 is the system identifier**:

- Incorrect. This is an incomplete and incorrect part of the System Identifier.

**Conclusion**:

The correct part of the address that represents the System Identifier is:

**A. 00a0.c96b.c490 is the system identifier.**

**Reference**:

- Juniper Networks Documentation on IS-IS: [IS-IS Configuration](https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/isis-configuring.html)

- ISO/IEC 10589, the IS-IS routing protocol standard.