Juniper JN0-664 Practice Exam Questions & Answers

BGP route target filtering can be configured on PE devices or on route reflectors (RRs). Configuring BGP route target filtering on RRs is more efficient and scalable, as it reduces the number of BGP sessions and updates between PE devices. To configure BGP route target filtering on RRs, the following steps are required:

Configure the family route-target statement under the BGP group or neighbor configuration on the RRs. This enables the exchange of the route-target address family between the RRs and their clients (PE devices). Configure the resolution rib bgp.l3vpn.0 resolution-ribs inet.0 statement under the routing-options configuration on the RRs. This enables the RRs to resolve next hops for VPN routes using the inet.0 routing table.

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.

Junos platforms use different mechanisms to evaluate incoming traffic for CoS purposes, such as:

Behavior aggregate classifiers: These classifiers use a single field in a packet header to classify traffic into different forwarding classes and loss priorities based on predefined or user-defined values.

Fixed classifiers: These classifiers use a fixed field in a packet header to classify traffic into different forwarding classes and loss priorities based on predefined values.

Multifield classifiers: These classifiers use multiple fields in a packet header to classify traffic into different forwarding classes and loss priorities based on user-defined values and filters.

Rewrite rules and traffic shapers are not used to evaluate incoming traffic for CoS purposes, but rather to modify or shape outgoing traffic based on CoS policies.

In the exhibit, we see an internal BGP (iBGP) setup within AS 65512, and an external BGP (eBGP) connection between R3 and ISP-A (AS 65511). The questions focus on the behavior of BGP routes advertised from R3 to R1 within the same AS.

1. **BGP Next-Hop Attribute (Option A and D)**:

- In iBGP, the next-hop attribute is **not** changed when a route is advertised to another iBGP peer. This means that when R3 advertises a route to R1, it retains the original next-hop value as learned from the eBGP peer (ISP-A).

- Therefore, Option D is correct: 'By default, the next-hop value for these routes is not changed by R3 before being sent to R1.'

2. **BGP Attributes (Option B and C)**:

- BGP attributes such as local preference, AS-path, and others are crucial for BGP route selection. The local preference attribute is used within an AS to indicate the preferred path for outbound traffic.

- When R3 advertises BGP routes to R1, it includes the local preference value assigned to those routes. This value is not removed and is propagated within the iBGP mesh.

- Therefore, Option C is correct: 'By default, the BGP local-preference value that is assigned on R3 is advertised to R1.'

**Reference**:

- Juniper Networks documentation on BGP behavior provides detailed insights into the propagation of BGP attributes within iBGP and eBGP contexts. Specifically, the Junos OS documentation covers the default behavior of next-hop and local preference attributes in BGP configurations.

- Junos OS BGP Configuration Guide: [Junos OS BGP Configuration Guide](https://www.juniper.net/documentation/en_US/junos/topics/concept/bgp-overview.html)

- For a deeper understanding of BGP attributes and their default behaviors, the 'Juniper Networks Day One: Exploring BGP' book is an excellent resource.

PIM sparse mode (PIM-SM) is a multicast routing protocol that uses a pull model to deliver multicast traffic. In PIM-SM, routers with receivers send join messages to their upstream neighbors toward a rendezvous point (RP) or a source-specific tree (SPT). The RP or SPT acts as the root of a shared distribution tree for a multicast group. Traffic is only forwarded to routers that request to join the distribution tree by sending join messages. PIM-SM does not flood traffic to all routers or prune routers without receivers, as PIM dense mode does.