JNCIS-ENT Practice Test 3 — 25 Questions

Question 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

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.

Question 11

Which Junos configuration command enables Dynamic ARP Inspection (DAI) for a specific VLAN named 'VLAN10'?

Accepted Answer

set ethernet-switching-options secure-access-port vlan VLAN10 arp-inspection. DAI is enabled under ethernet-switching-options secure-access-port vlan for the specific VLAN name.

Answer

set protocols arp-inspection vlan VLAN10

Answer

set vlans VLAN10 dynamic-arp-inspection

Answer

set interfaces vlan unit 10 family inet arp-inspection

Question 12

When configuring VRRP on a Juniper router, what IP address must be assigned as the virtual IP address for the group?

Accepted Answer

An IP address belonging to the same subnet as the physical interface connected to the broadcast domain.. The virtual IP address must belong to the same subnet as the physical interface IP address configured on the participating routers.

Answer

A loopback IP address configured on the master Routing Engine.

Answer

A public IP address provided by your upstream Internet Service Provider.

Answer

A reserved multicast address in the 224.0.0.18 range.

Question 13

When should you consider increasing the 'csnp-interval'?

Accepted Answer

To reduce control traffic overhead on slow links.. Increasing the interval is useful on slow or congested links to reduce the frequency of full database synchronization traffic.

Answer

To improve convergence time.

Answer

To increase the maximum LSP size.

Answer

To fix adjacency flapping.

Question 14

An engineer configures Nonstop Active Routing (NSR) on an MX series router. What is required for NSR to function properly on BGP peering sessions?

Accepted Answer

GRES must be enabled at the chassis level, and NSR must be explicitly enabled under the BGP protocol hierarchy.. NSR requires GRES enabled at the chassis level and NSR configured specifically under the routing-options protocols bfgp hierarchy.

Answer

Graceful Restart must be disabled globally on all routers.

Answer

VRRP must be configured on all BGP peering interfaces.

Answer

LACP fast mode must be enabled on all physical uplinks.

Question 15

Which THREE actions occur when a BGP speaker receives a Notification message from a peer? (Choose three.)

Accepted Answer

The TCP connection associated with the BGP session is closed.. When a BGP Notification message is received, it indicates an error condition. The receiving router moves the session to Idle, closes the TCP connection, and clears all routes learned from that peer.

Answer

A Keepalive message is immediately sent in response to acknowledge the error.

Answer

The peer router automatically re-establishes the connection without applying the connect retry timer.

Question 16

What is the purpose of the 'lsp-lifetime' command?

Accepted Answer

To set the duration for which an LSP is valid.. The 'lsp-lifetime' command sets the duration after which an LSP is considered invalid if not refreshed.

Answer

To define how often the DIS sends Hellos.

Answer

To limit the number of LSPs in the database.

Answer

To set how long the adjacency stays up.

Question 17

Which command displays the status of Virtual Chassis member switches, their roles, and their serial numbers on an EX series switch?

Accepted Answer

show virtual-chassis. The 'show virtual-chassis' command is the primary operational command to view member status, roles (Master/Backup/Linecard), and IDs.

Answer

show lacp statistics

Answer

show vrrp summary

Question 18

Which operational command allows you to view the real-time status of LACP packet exchanges and partner system IDs for an aggregated interface on a Junos switch?

Accepted Answer

show lacp interface. The 'show lacp interface' command displays detailed LACP partner information, partner port numbers, and state flags.

Answer

show interfaces ae0 statistics

Answer

show chassis lacp-status

Answer

show vrrp lacp-summary

Question 19

You are analyzing a core Juniper MX router after an ISSU upgrade procedure completed. You notice that BGP sessions dropped immediately after the final routing engine rebooted. What post-upgrade verification step should have been performed to prevent unexpected protocol drops during ISSU?

Accepted Answer

Verify that all external BGP peers negotiated Graceful Restart capability and that helper mode was active on both ends prior to initiating the upgrade.. Verifying that BGP graceful restart and helper modes were fully operational and peer routers had acknowledged the capability before starting ISSU.

Answer

Confirm that LACP minimum-links is set to zero.

Answer

Check that the Virtual Chassis cable is connected between the MX Routing Engines.

Answer

Ensure VRRP preemption is turned off on all core interfaces.

Question 20

Which CLI command displays the packet statistics, errors, and drop counters for a Link Aggregation Group (LAG) named ae0?

Accepted Answer

show interfaces ae0. The 'show interfaces ae0' command displays general interface statistics, error counts, and drops for the aggregated interface.

Answer

show chassis interface-drops ae0

Answer

show virtual-chassis interface ae0

Answer

show lacp statistics ae0