Free Juniper JN0-664 Practice Exam with Questions & Answers

Understanding the Exhibit and the Problem Statement

The diagram shows a Layer 3 VPN (L3VPN) setup where multiple customers (Customer A, B, and C) are connected across a service provider network using PE (Provider Edge) routers.

PE1 and PE2 exchange VPN routes for all customers using BGP/MPLS Layer 3 VPN (L3VPN) routing.

The question asks how to verify if PE2 is receiving VPN routes for Customer C.

Evaluating the Answer Choices

✅ B. show route table bgp.l3vpn.0 (Correct Answer)

Why?

This command shows all VPN routes stored in the BGP Layer 3 VPN table (bgp.l3vpn.0).

Since PE routers exchange VPN routes using MP-BGP, this table contains the VPN-IPv4 or VPN-IPv6 routes for all customers.

If PE2 is receiving routes from PE1 for Customer C, they will appear in bgp.l3vpn.0.

❌ A. show route table inet.0 (Incorrect)

Why?

The inet.0 table contains global unicast routes for the service provider's network.

VPN routes do not appear here because they are stored in VRF-specific tables.

This command won’t help verify VPN route exchange between PE1 and PE2.

❌ C. show route table customer-c.inet.0 (Incorrect)

Why?

The table customer-c.inet.0 represents the VRF routing table for Customer C on the local PE.

It only shows locally installed routes for Customer C but does not confirm if PE2 is receiving routes from PE1.

This command is useful to check local VPN routing but not BGP route propagation.

❌ D. show route summary (Incorrect)

Why?

This command only provides a summary of route counts per protocol (BGP, OSPF, etc.).

It does not display specific VPN routes.

It is useful for general troubleshooting but doesn’t confirm VPN route receipt.

Final Answer: ✅ show route table bgp.l3vpn.0 (Option B)

Official Juniper Documentation Reference

Junos MPLS VPNs Configuration Guide???? Juniper Documentation

"The show route table bgp.l3vpn.0 command displays all VPN-IPv4 routes learned via MP-BGP for Layer 3 VPNs."

A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone. To create a sham link, you need to configure the local and remote addresses of the PE routers under the [edit protocols ospf area area-id] hierarchy level1.

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospfv2-sham-links.html

Option A (Correct):

In IS-IS, the Designated Intermediate System (DIS) is elected based on the highest configured priority (as defined in Junos OS).

If priorities are equal, the router with the highest MAC address becomes the DIS.

A priority value of 10 will always override a lower priority (e.g., 1).

A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone. A sham link creates an OSPF multihop neighborship between the PE routers using TCP port 646. The PEs exchange Type 1 OSPF LSAs instead of Type 3 OSPF LSAs for the L3VPN routes, which allows OSPF to use the correct metric for route selection1.

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.**

**References**:

- 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.

Route reflection is a BGP feature that allows a router to reflect routes learned from one IBGP peer to another IBGP peer, without requiring a full-mesh IBGP topology. Route reflectors do not change any existing BGP attributes by default when advertising routes, unless explicitly configured to do so. A BGP peer does not require any configuration changes to become a route reflector client, only the route reflector needs to be configured with the client parameter under [edit protocols bgp group group-name neighbor neighbor-address] hierarchy level.

The vrf-target statement is used in routing-instances to define route-target communities for VPN route import and export policies.

vrf-target export → Controls which route targets (RTs) are added to advertised routes (used when sending routes to remote PEs).

vrf-target import → Controls which VPN routes are accepted into the VRF (used when receiving routes from remote PEs).

https://www.juniper.net/documentation/us/en/software/junos/traffic-mgmt-qfx/topics/concept/cos-qfx-series-default-scheduling-classification-understanding.html

The auto-export parameter is a routing option that allows a routing instance to share routes with other routing instances or the master routing table. The auto-export parameter automatically exports routes from one routing instance to another based on the route target communities attached to the routes. In this scenario, the 10.101.1.0/24 route will be shared if the auto-export parameter is configured under [edit routing-options] hierarchy level.

Prefer the route with the lower origin code. Routes learned from an IGP have a lower origin code than those learned from an exterior gateway protocol (EGP), and both have lower origin codes than incomplete routes (routes whose origin is unknown). https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/bgp/topics/concept/routing-protocols-address-representation.html