JNCIS-ENT Practice Exam 3 — 20 Questions

Question 1

Which TCP port is used by BGP to establish communication between peers?

Accepted Answer

TCP 179. BGP operates over TCP port 179.

Answer

UDP 520

Answer

TCP 80

Answer

TCP 500

Question 2

Which THREE path attributes are classified as 'well-known mandatory'? (Choose three)

Accepted Answer

NEXT_HOP. The well-known mandatory attributes in BGP are ORIGIN, AS_PATH, and NEXT_HOP. Local Preference is well-known discretionary, and MED is optional non-transitive.

Answer

MED

Answer

LOCAL_PREF

Question 3

Which THREE statements are true regarding OSPF Graceful Restart helper mode on Juniper routers? (Choose three)

Accepted Answer

It helps prevent unnecessary SPF recalculations across the network during transient control plane restarts.. Helper mode allows routers to maintain routing tables while neighbors restart, suppressing routing churn and dropping adjacencies prematurely.

Answer

It forces the restarting router to immediately drop all data forwarding traffic.

Answer

It requires manual configuration of VRRP tracking on all loopback interfaces.

Question 4

A BGP speaker receives an UPDATE message containing a malformed attribute. According to BGP specifications, which action does the receiving router take?

Accepted Answer

Send a NOTIFICATION message and terminate the BGP session.. A malformed attribute or critical error triggers a NOTIFICATION message with an appropriate error code, followed by session teardown.

Answer

Strip the attribute and propagate the route to iBGP peers.

Answer

Send an UPDATE message requesting retransmission.

Answer

Silently ignore the attribute and install the route.

Question 5

How do you configure an interface to be point-to-point when using IS-IS?

Accepted Answer

set protocols isis interface point-to-point. You use the 'set protocols isis interface point-to-point' command to force point-to-point mode.

Answer

set protocols isis interface-type point-to-point

Answer

set interfaces <name> unit 0 family iso point-to-point

Answer

set protocols isis link-type p2p

Question 6

Which command displays the IS-IS interface parameters?

Accepted Answer

show isis interface. 'show isis interface' shows the configuration and state of IS-IS interfaces.

Answer

show isis configuration

Answer

show interfaces isis

Answer

show protocols isis interface

Question 7

Which BGP attribute is classified as 'well-known discretionary'?

Accepted Answer

LOCAL_PREF. Local Preference is a well-known discretionary attribute, meaning all BGP implementations must recognize it, but it does not have to be included in every update.

Answer

AS_PATH

Answer

ORIGIN

Answer

MED

Question 8

Which TWO statements are true regarding BGP communities in Junos? (Choose two)

Accepted Answer

Communities are optional transitive path attributes.. Communities can be standard (32-bit values represented as AS:value) or extended, and they are used to group routes for policy enforcement.

Answer

Communities replace the AS_PATH attribute entirely.

Answer

Communities are evaluated after the router ID tie-breaker.

Answer

Communities can only be applied to eBGP sessions and are stripped on iBGP.

Question 9

You are configuring multi-topology IS-IS. What does this allow?

Accepted Answer

Running separate topologies for different address families.. Multi-topology IS-IS allows for separate routing topologies for different protocol families (e.g., IPv4 and IPv6).

Answer

Load balancing over different physical paths.

Answer

Creating multiple areas within a single instance.

Answer

Increasing the maximum MTU.

Question 10

Which TWO items are required when configuring VRRP on a Juniper router interface? (Choose two)

Accepted Answer

At least one virtual IP address configured to act as the default gateway for clients.. VRRP configuration requires a Virtual Router ID (VRID) and at least one virtual IP address.

Answer

A static BGP peering session to an upstream provider.

Answer

A pre-configured GRES license on the Routing Engine.

Answer

An active LACP aggregated Ethernet bundle.

Question 11

An engineer configures a BGP policy to set the MED attribute on routes advertised to an eBGP peer. What is the primary purpose of the MED (Multi-Exit Discriminator) attribute?

Accepted Answer

To indicate to an external AS which entry point is preferred for traffic entering the local AS.. MED is an optional non-transitive attribute used to inform external peers about the preferred entry point into an AS.

Answer

To dictate the preferred path for traffic leaving the local AS.

Answer

To prevent routing loops across multiple autonomous systems.

Answer

To assign a priority score for internal route selection within the same AS.

Question 12

When troubleshooting a BGP routing loop or unexpected route suppression, which THREE Junos operational commands provide visibility into BGP path attributes and decision processes? (Choose three)

Accepted Answer

show route extensive. Detailed route inspection and BGP neighbor debugging commands include 'show route extensive', 'show bgp neighbor', and 'show route protocol bgp'.

Answer

show ldp database

Answer

show ospf interface

Question 13

Which BGP message type is responsible for negotiating session parameters, including autonomous system numbers, hold times, and BGP identifiers during session establishment?

Accepted Answer

Open. The BGP Open message is the first message sent after a TCP connection is established. It contains parameters such as the BGP version, local AS number, hold time, BGP identifier, and optional parameters (capabilities).

Answer

Notification

Answer

Update

Answer

Keepalive

Question 14

During an audit of a Juniper EX4300 Virtual Chassis, you notice that member 1 and member 2 are connected via mixed 1G and 10G uplink ports. How does Junos handle mixed-speed Virtual Chassis port configurations?

Accepted Answer

Virtual Chassis ports (VCPs) must be explicitly configured to match supported transceiver speeds, and mixing unsupported interface types will result in port initialization failure.. Junos EX series virtual chassis ports can be configured for specific speeds, but mismatched or unsupported port combinations will cause initialization failures or link errors depending on the platform.

Answer

Mixed speed links automatically drop to 1G to maintain backward compatibility without administrative intervention.

Answer

Junos automatically load-balances stacking traffic across 1G and 10G links using weighted round-robin.

Answer

Only the 10G ports will carry control plane traffic while 1G ports are restricted to data transit.

Question 15

An administrator is setting up VRRP tracking on an EX4300 switch interface. If the uplink interface monitoring the core network fails, what should happen to the VRRP priority on the gateway interface?

Accepted Answer

The VRRP priority is decremented by a configured value so that the backup router can assume the master role.. VRRP interface tracking automatically decrements the local router's priority when a monitored tracking interface goes down, allowing a backup router with higher priority to take over as master.

Answer

The VRRP priority is increased to maximum to force immediate forwarding.

Answer

The interface shuts down all LACP bundles connected to the switch.

Answer

The switch initiates an immediate In-Service Software Upgrade.

Question 16

An engineer configures a LAG between an EX4300 switch and a server. The server uses static LAG mode (no LACP). How must the Junos switch interface be configured to successfully form the bundle?

Accepted Answer

Omit the LACP protocol configuration under the aggregated-ether-options stanza, operating in static mode.. When connecting to a device that does not support LACP, you must configure the Junos aggregated interface without LACP (manual/static mode).

Answer

Configure VRRP on the ae0 interface to manage the static bundle.

Answer

Configure LACP passive mode on the EX4300 switch.

Answer

Enable Graceful Restart on the physical ports.

Question 17

Which TWO statements accurately describe the behavior of the BGP AS_PATH attribute? (Choose two)

Accepted Answer

It is a well-known mandatory attribute.. AS_PATH is well-known mandatory and gets prepended with the local AS number every time an update leaves an Autonomous System via eBGP.

Answer

It is automatically stripped when crossing a confederation boundary.

Answer

It is modified when an update is sent to an iBGP peer.

Answer

It is an optional non-transitive attribute used for internal metrics.

Question 18

Which TWO options represent valid benefits of configuring Link Aggregation Groups (LAG)? (Choose two)

Accepted Answer

Increased aggregate bandwidth between connected networking devices.. LAGs provide increased aggregate bandwidth and link redundancy/failover.

Answer

Synchronization of BGP routing daemon state between separate routers.

Answer

Automatic upgrade of Junos OS across peer devices.

Answer

Elimination of the need for Spanning Tree Protocol across all VLANs.

Question 19

Which THREE potential issues can arise if LACP is misconfigured between a Juniper switch and a connected peer device? (Choose three)

Accepted Answer

Traffic loops may occur if static LAG mode is mismatched with LACP active mode on opposite ends.. LACP misconfigurations can lead to link suspension, flapping due to timeout mismatches, or bundle failure if minimum links aren't met.

Answer

GRES will be disabled on the routing engine automatically.

Answer

The switch will automatically trigger an In-Service Software Upgrade (ISSU) to fix the mismatch.

Question 20

An administrator configures BGP multipath on a Junos router. Which THREE conditions must be met for BGP paths to be considered equal and installed as multipaths? (Choose three)

Accepted Answer

The paths must have the same Local Preference value.. For BGP multipath, paths must typically have matching AS path lengths (unless relaxation is on), matching local preference, matching MED, and matching origin, and the next-hop router must resolve via the same IGP metric cost.

Answer

The paths must originate from different Autonomous Systems entirely.

Answer

The router IDs of the advertising routers must be identical.