JN0-351 Enterprise Routing and Switching, Specialist Exam

Exam Details
Exam questions are derived from the recommended training and the exam resources listed above. Pass/fail status is available immediately after taking the exam. The exam is only provided in English.

Exam Code JN0-351
Prerequisite Certification JNCIA-Junos
Delivered by
Exam Length 90 minutes
Exam Type 65 multiple-choice questions
Software Versions Junos 23.1

Recertification
Juniper certifications are valid for three years. For more information, see Recertification.

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Exam Objectives
Here’s a high-level view of the skillset required to successfully complete the JNCIS-ENT certification exam.

Exam Objective

Description
Layer 2 Switching or VLANs

Identify the concepts, operations, or functionalities of Layer 2 switching for the Junos OS:
Bridging components
Frame processing

Describe the concepts, benefits, or functionalities of VLANs:
Ports
Tagging
Native VLANs and voice VLANs
Inter-VLAN routing

Demonstrate knowledge how to configure, monitor, or troubleshoot Layer 2 switching or VLANs:
Interfaces and ports
VLANs
Inter-VLAN routing

Spanning Tree
Describe the concepts, benefits, operations, or functionalities of the Spanning Tree Protocol (STP):

STP and Rapid Spanning Tree Protocol (RSTP) concepts
Port roles and states
Bridge Protocol Data Units (BPDUs)
Convergence and reconvergence

Demonstrate knowledge how to configure, monitor, or troubleshoot Spanning Tree:
STP
RSTP

Layer 2 Security

Identify the concepts, benefits, or operations of various Layer 2 protection or security features:
BPDU, loop or root protection
Port security, including MAC limiting, DHCP snooping, Dynamic ARP inspection (DAI) or IP source guard
MACsec
Storm control

Identify the concepts, benefits, or operations of Layer 2 firewall filters:
Filter types
Processing order
Match criteria and actions

Demonstrate knowledge how to configure, monitor, or troubleshoot Layer 2 security:
Protection
Port security
Storm control
Firewall filter configuration and application

Protocol Independent Routing

Identify the concepts, operations, or functionalities of various protocol-independent routing components:
Static, aggregate, and generated routes
Martian addresses
Routing instances, including routing information base (RIB) groups
Load balancing
Filter-based forwarding

Demonstrate knowledge how to configure, monitor, or troubleshoot various protocol-independent routing components:
Static, aggregate, and generated routes
Load balancing
Filter-based forwarding

OSPF
Describe the concepts, operations, or functionalities of OSPF:

Link-state database
OSPF packet types
Router ID
Adjacencies and neighbors
Designated router (DR) and backup designated router (BDR)
OSPF area and router types
Realms
Link-state advertisement (LSA) packet types

Demonstrate knowledge how to configure, monitor, or troubleshoot OSPF:
Areas, interfaces, and neighbors
Additional basic options
Routing policy application
Troubleshooting tools (ping, traceroute, traceoptions, show commands, logging)

IS-IS

Describe the concepts, operations, or functionalities of IS-IS:
Link-state database
IS-IS Protocol Data Units (PDUs)
Type, length, and values (TLVs)
Adjacencies and neighbors
Levels and areas
Designated intermediate system (DIS)
Metrics

Demonstrate knowledge of how to configure, monitor, or troubleshoot IS-IS:
Levels, interfaces, and adjacencies
Additional basic options
Routing policy application
Troubleshooting tools (ping, traceroute, traceoptions, show commands, logging)

BGP

Describe the concepts, operations, or functionalities of BGP:
BGP basic operation
BGP message types
Attributes
Route/path selection process
Internal and external BGP (IBGP and EBGP) functionality and interaction

Demonstrate knowledge of how to configure, monitor, or troubleshoot BGP:
Groups and peers
Additional basic options
Routing policy application
Troubleshooting tools (ping, traceroute, traceoptions, show commands, logging)

Tunnels

Identify the concepts, requirements, or functionalities of IP tunneling:
Tunneling applications and considerations
Generic Routing Encapsulation (GRE)
IP-IP

Demonstrate knowledge of how to configure, monitor, or troubleshoot IP tunnels:
GRE
IP-IP
Troubleshooting tools (ping, traceroute, traceoptions, show commands, logging)

High Availability

Identify the concepts, benefits, applications, or requirements for high availability in a Junos OS environment:
Link aggregation groups (LAG)
Redundant trunk groups (RTG)
Virtual chassis
Graceful restart
Graceful Routing Engine switchover (GRES)
Nonstop active routing (NSR)
Nonstop bridging (NSB)
Bidirectional Forwarding Detection (BFD)
Virtual Router Redundancy Protocol (VRRP)
Unified In-Service Software Upgrade (ISSU)

Demonstrate knowledge of how to configure, monitor, or troubleshoot high availability components:
LAG and RTG
Virtual chassis
Graceful restart, GRES, NSB, and NSR
VRRP
ISSU
Troubleshooting tools (traceoptions, show commands, logging)

Exam Preparation
We recommend the following resources to help you prepare for your exam. However, these resources aren’t required, and using them doesn’t guarantee you’ll pass the exam.

Recommended Training
Junos Intermediate Routing
Junos Enterprise Switching

Exam Resources
Industry/product knowledge
Juniper TechLibrary

Additional Preparation

Juniper Learning Portal
This track enables you to demonstrate competence with networking technology in general and Juniper Networks enterprise routing and switching platforms. JNCIS-ENT, the specialist-level certification in this track, is designed for experienced networking professionals with beginner to intermediate knowledge of routing and switching implementations in Junos. The written exam verifies your basic understanding of routing and switching technologies and related platform configuration and troubleshooting skills.

This track includes four certifications:
JNCIA-Junos: Junos, Associate. For details, see JNCIA-Junos.
JNCIS-ENT: Enterprise Routing and Switching, Specialist. For details, see the sections below.
JNCIP-ENT: Enterprise Routing and Switching, Professional. For details, see JNCIP-ENT.
JNCIE-ENT: Enterprise Routing and Switching, Expert. For details, see JNCIE-ENT.

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Sample Questions and Answers

QUESTION 1
Exhibit.
Which router will become the OSPF BDR if all routers are powered on at the same time?

A. R4
B. R1
C. R3
D. R2

Answer: A

Explanation:
OSPF DR/BDR election is a process that occurs on multi-access data links. It is intended to select two
OSPF nodes: one to be acting as the Designated Router (DR), and another to be acting as the Backup
Designated Router (BDR). The DR and BDR are responsible for generating network LSAs for the multiaccess
network and synchronizing the LSDB with other routers on the same network1.
The DR/BDR election is based on two criteria: the OSPF priority and the router ID. The OSPF priority
is a value between 0 and 255 that can be configured on each interface participating in OSPF. The
default priority is 1. A priority of 0 means that the router will not participate in the election and will
never become a DR or BDR. The router with the highest priority will become the DR, and the router
with the second highest priority will become the BDR. If there is a tie in priority, then the router ID is
used as a tie-breaker. The router ID is a 32-bit number that uniquely identifies each router in an OSPF
domain. It can be manually configured or automatically derived from the highest IP address on a
loopback interface or any active interface2.
In this scenario, all routers have the same priority of 1, so the router ID will determine the outcome
of the election. The router IDs are shown in the exhibit as RID values. The highest RID belongs to R4
(10.10.10.4), so R4 will become the DR. The second highest RID belongs to R3 (10.10.10.3), so R3 will become the BDR.
Reference:
1: OSPF DR/BDR Election: Process, Configuration, and Tuning 2: OSPF Designated Router (DR) and
Backup Designated Router (BDR)

QUESTION 2
Exhibit.
What is the management IP address of the device shown in the exhibit?

A. 10.210.20.233
B. 172.23.12.100
C. 128.0.0.1
D. 172.23.11.10

Answer: B

Explanation:
The management IP address of a device is the IP address that is used to access the device for
configuration and monitoring purposes. It is usually assigned to a dedicated management interface
that is separate from the data interfaces. The management interface can be accessed via SSH, Telnet,
HTTP, or other protocols.
In the exhibit, the list of interfaces and their statuses shows that the management interface is me0.
This interface has an admin status of up, a protocol status of inet, a local address of
172.23.12.100, and a remote address of unspecified. This means that the me0 interface is active,
has an IPv4 address assigned, and is not connected to another device.
Therefore, the management IP address of the device shown in the exhibit is 172.23.12.100.
Reference:
: [Management Interfaces Overview] : [Displaying Interface Status Information]

QUESTION 3
Which three protocols support BFD? (Choose three.)

A. RSTP
B. BGP
C. OSPF
D. LACP
F. FTP

Answer: BCD

Explanation:
BFD is a protocol that can be used to quickly detect failures in the forwarding path between two
adjacent routers or switches. BFD can be integrated with various routing protocols and link
aggregation protocols to provide faster convergence and fault recovery.
According to the Juniper Networks documentation, the following protocols support BFD on Junos OS
devices1:
BGP: BFD can be used to monitor the connectivity between BGP peers and trigger a session reset if a
failure is detected. BFD can be configured for both internal and external BGP sessions, as well as for
IPv4 and IPv6 address families2.
OSPF: BFD can be used to monitor the connectivity between OSPF neighbors and trigger a state
change if a failure is detected. BFD can be configured for both OSPFv2 and OSPFv3 protocols, as well
as for point-to-point and broadcast network types3.
LACP: BFD can be used to monitor the connectivity between LACP members and trigger a link state
change if a failure is detected. BFD can be configured for both active and passive LACP modes, as
well as for static and dynamic LAGs4.
Other protocols that support BFD on Junos OS devices are:
IS-IS: BFD can be used to monitor the connectivity between IS-IS neighbors and trigger a state change
if a failure is detected. BFD can be configured for both level 1 and level 2 IS-IS adjacencies, as well as
for point-to-point and broadcast network types.
RIP: BFD can be used to monitor the connectivity between RIP neighbors and trigger a route update
if a failure is detected. BFD can be configured for both RIP version 1 and version 2 protocols, as well
as for IPv4 and IPv6 address families.
VRRP: BFD can be used to monitor the connectivity between VRRP routers and trigger a priority
change if a failure is detected. BFD can be configured for both VRRP version 2 and version 3
protocols, as well as for IPv4 and IPv6 address families.
The protocols that do not support BFD on Junos OS devices are:
RSTP: RSTP is a spanning tree protocol that provides loop prevention and rapid convergence in layer 2
networks. RSTP does not use BFD to detect link failures, but relies on its own hello mechanism that
sends BPDU packets every 2 seconds by default.
FTP: FTP is an application layer protocol that is used to transfer files between hosts over a TCP
connection. FTP does not use BFD to detect connection failures, but relies on TCPs own
retransmission and timeout mechanisms.
Reference:
1: [Configuring Bidirectional Forwarding Detection] 2: [Configuring Bidirectional Forwarding
Detection for BGP] 3: [Configuring Bidirectional Forwarding Detection for OSPF] 4: [Configuring
Bidirectional Forwarding Detection for Link Aggregation Control Protocol] : [Configuring Bidirectional
Forwarding Detection for IS-IS] : [Configuring Bidirectional Forwarding Detection for RIP] :
[Configuring Bidirectional Forwarding Detection for VRRP] : [Understanding Rapid Spanning Tree
Protocol] : [Understanding FTP]

QUESTION 4
Exhibit.
The ispi _ inet. 0 route table has currently no routes in it.
What will happen when you commit the configuration shown on the exhibit?

A. The inet. 0 route table will be completely overwritten by the ispi . inet. 0 route table.
B. The inet. 0 route table will be imported into the ispi . inet. 0 route table.
C. The ISPI . inet. 0 route table will be completely overwritten by the inet. o route table.
D. The ISPI . inet. 0 route table will be imported into the inet. 0 route table.

Answer: B

Explanation:
The configuration shown in the exhibit is an example of a routing instance of type virtual-router. A
routing instance is a collection of routing tables, interfaces, and routing protocol parameters that
create a separate routing domain on a Juniper device1. A virtual-router routing instance allows
administrators to divide a device into multiple independent virtual routers, each with its own routing
table2.
The configuration also includes a rib-group statement, which is used to import routes from one
routing table to another. A rib-group consists of an import-rib statement, which specifies the source
routing table, and an export-rib statement, which specifies the destination routing table.
In this case, the rib-group name is inet-to-ispi, and the import-rib statement specifies inet.0 as the
source routing table. The export-rib statement specifies ispi.inet.0 as the destination routing table.
This means that the routes from inet.0 will be imported into ispi.inet.0.
Therefore, the correct answer is B. The inet.0 route table will be imported into the ispi.inet.0 route table.
Reference:
1: Routing Instances Overview 2: Virtual Routing Instances : [rib-group (Routing Options)]

QUESTION 5
Which statement is correct about graceful Routing Engine switchover (GRES)?

A. The PFE restarts and the kernel and interface information is lost.
B. GRES has a helper mode and a restarting mode.
C. When combined with NSR, routing is preserved and the new master CK does not restart rpd.
D. With no other high availability features enabled, routing is preserved and the new master CK does not restart rpd.

Answer: C

Explanation:
The Graceful Routing Engine Switchover (GRES) feature in Junos OS enables a router with redundant
Routing Engines to continue forwarding packets, even if one Routing Engine fails1. GRES preserves
interface and kernel information, ensuring that traffic is not interrupted1. However, GRES does not
preserve the control plane1.
To preserve routing during a switchover, GRES must be combined with either Graceful Restart
protocol extensions or Nonstop Active Routing (NSR)1. When GRES is combined with NSR, nearly 75
percent of line rate worth of traffic per Packet Forwarding Engine remains uninterrupted during
GRES1. Any updates to the primary Routing Engine are replicated to the backup Routing Engine as
soon as they occur1.
Therefore, when GRES is combined with NSR, routing is preserved and the new master CK does not
restart rpd1.

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