JNCIS-ENT High Availability Practice Test 4 — 15 Questions

Question 1

An administrator is configuring VRRP on an EX4300 switch and wants to ensure that when the primary router recovers from a failure, it immediately reclaims the master role from the backup router. Which VRRP configuration parameter controls this behavior?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The preemption parameter (enabled by default), which allows a higher-priority router to preempt the current master.. Preemption is enabled by default in Junos VRRP, allowing a higher-priority router to take over when it comes back online.

Answer

The tracking decrement value set to zero.

Answer

The virtual-mac-address configuration statement.

Answer

The advertisement interval timer set to 1 millisecond.

Question 2

Which configuration command enables Graceful Routing Engine Switchover (GRES) globally on a Juniper routing platform?

Accepted Answer

set chassis redundancy graceful-switchover. GRES is enabled under the [edit chassis redundancy graceful-switchover] hierarchy in Junos.

Answer

set routing-options gres enable

Answer

set interfaces redundancy gres

Answer

set system graceful-restart

Question 3

You are troubleshooting an issue where an EX4300 Virtual Chassis fails to boot after adding a new switch member. The system console displays errors regarding incompatible Junos images and hardware mismatch on the Virtual Chassis ports. What is the correct procedure to recover and integrate the new member?

Accepted Answer

Isolate the new switch, boot it independently, upgrade/downgrade its Junos OS version to match the master switch, and then connect it to the Virtual Chassis ring.. The EX4300 Virtual Chassis requires all member switches to run the same Junos OS release; a mismatch triggers boot failure and VCP errors. The correct recovery is to isolate the new member, boot it standalone, install the matching Junos image, and only then reconnect it to the Virtual Chassis ring. This ensures the master can synchronize the member without image incompatibility. Option A is the only procedure that directly resolves the root cause.

Answer

Configure GRES on the replacement switch using the CLI before connecting stacking cables.

Answer

Disable LACP on all aggregated links across the stack.

Answer

Factory reset all existing switches in the Virtual Chassis via the master console.

Question 4

Which operational command displays the configured member IDs, priorities, and roles in an EX Series Virtual Chassis?

Accepted Answer

show virtual-chassis. The 'show virtual-chassis' command displays member IDs, roles, priorities, and serial numbers.

Answer

show lacp aggregated-devices

Answer

show chassis alarms

Answer

show vrrp mastership

Question 5

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

Question 6

You are troubleshooting a VRRP deployment where two EX4600 switches are acting as redundant gateways for several VLANs. Clients on VLAN 10 report intermittent gateway unreachability. You notice that VRRP mastership frequently flips between Switch A and Switch B. What is the most effective way to stabilize VRRP mastership?

Accepted Answer

Review interface error counters, ensure physical link stability, and increase the VRRP advertisement interval if transient congestion is dropping packets.. Frequent VRRP mastership flips are almost always caused by missed advertisements due to physical link instability or transient congestion. Reviewing interface error counters and increasing the VRRP advertisement interval (if congestion is dropping packets) stabilizes mastership without altering priority. This addresses the root cause rather than masking it with unrelated features.

Answer

Configure all member ports in the LAG to use static mode.

Answer

Disable Virtual Chassis on both switches.

Answer

Remove GRES from the routing engine configuration.

Question 7

Which CLI command displays the operational status and roles of all members in a Juniper EX Series Virtual Chassis?

Accepted Answer

show virtual-chassis. The 'show virtual-chassis' command displays the role (Master, Backup, Linecard) of each member.

Answer

show chassis vcp

Answer

show lacp virtual-chassis

Answer

show vrrp chassis

Question 8

An administrator configures a Link Aggregation Group (LAG) using LACP between two EX series switches. The link fails to aggregate, and the log shows 'LACP status: Expired'. What does the 'Expired' state indicate?

Accepted Answer

The local port has stopped receiving LACP packets from the remote peer within the timeout window.. The 'Expired' state in LACP means the local port has stopped receiving LACP packets from the remote peer within the expected timeout period.

Answer

The Virtual Chassis primary routing engine license has expired.

Answer

The Junos software license for aggregated Ethernet has expired.

Answer

The GRES synchronization timer has timed out.

Question 9

Which THREE statements accurately describe the behavior and configuration of VRRP tracking on Junos devices? (Choose three)

Accepted Answer

If the decremented priority falls below the backup router's priority, mastership transitions to the backup router.. Option E is correct because VRRP tracking on Junos is designed to decrement the router's VRRP priority by a configured amount when a tracked interface or route becomes unavailable, reflecting degraded forwarding capability. Option A is correct because once the priority is decremented below that of a backup router, the backup with the higher priority takes over as master, triggering a mastership transition. Option C is correct because Junos VRRP tracking supports monitoring multiple interfaces or reachability paths simultaneously within a single tracking configuration, allowing comprehensive failure detection. Option B is incorrect because tracking only adjusts priority; it does not administratively shut down the tracked interface. Option D is incorrect because tracking has no automatic effect on GRES (Graceful Routing Engine Switchover) and does not disable it.

Answer

Tracking forces the tracked interface to shut down permanently when a failure occurs.

Answer

Tracking automatically disables GRES on the routing engine.

Question 10

Which TWO commands are used to verify link aggregation and LACP operational status on a Juniper switch? (Choose two)

Accepted Answer

show interfaces ae0. Option C, 'show interfaces ae0', is correct because the aggregated Ethernet (ae) interface is the logical bundle created by link aggregation, and this command displays its operational status, member links, and whether the bundle is up. Option D, 'show lacp interface', is correct because it directly reports LACP protocol state per member interface, including actor/partner state flags (such as whether the link is collecting and distributing) and LACP operational status. Option A, 'show virtual-chassis', is unrelated since it displays Virtual Chassis topology and member roles, not link aggregation. Option B, 'show vrrp detail', concerns VRRP redundancy state and has nothing to do with LACP or aggregation. Option E, 'show chassis routing-engine', reports Routing Engine status and resources, not link aggregation or LACP.

Answer

show virtual-chassis

Answer

show vrrp detail

Answer

show chassis routing-engine

Question 11

Which THREE conditions must be met to successfully execute an In-Service Software Upgrade (ISSU) on a dual-RE Juniper routing platform? (Choose three)

Accepted Answer

Both Routing Engines must be fully populated with identical hardware models and supported Junos images.. Option A is correct because ISSU requires both Routing Engines to be the same hardware model and to run compatible, supported Junos images so that the upgraded RE can take over cleanly. Option B is correct because Graceful Routing Engine Switchover (GRES) must be enabled and synchronized, allowing the backup RE to assume control without resetting the data plane or losing forwarding state. Option E is correct because Nonstop Active Routing (NSR) or Graceful Restart must be configured for the active routing protocols so that routing adjacencies and protocol state survive the RE switchover during the upgrade. Option C is incorrect because ISSU is designed to avoid taking down all physical interfaces; interfaces remain forwarding during the upgrade. Option D is incorrect because VRRP preemption settings are not a prerequisite for ISSU and do not need to be disabled.

Answer

All physical interfaces must be manually placed in a disabled state prior to upgrade.

Answer

VRRP preemption must be disabled on all routing interfaces.

Question 12

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

Accepted Answer

Increased aggregate bandwidth between connected networking devices.. Option A is correct because a Link Aggregation Group bundles multiple physical interfaces into a single logical link, so the combined throughput of the member links provides increased aggregate bandwidth between the connected devices. Option D is correct because LAG monitors member link health and, if one physical member link fails, traffic is automatically redistributed across the remaining active links, providing redundancy and failover without losing the logical interface. Option B is incorrect because BGP peer state synchronization is handled by BGP itself (e.g., via TCP sessions and route reflectors), not by LAG. Option C is incorrect because Junos OS upgrades are performed through software management procedures, not through link aggregation. Option E is incorrect because LAG does not eliminate the need for Spanning Tree Protocol in all cases; STP may still be required to prevent loops in topologies with redundant paths outside the LAG.

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 13

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.. Option A is correct because VRRP requires at least one virtual IP address on the interface, which serves as the shared default gateway that hosts on the subnet point to; the master router owns this VIP and answers ARP for it. Option B is correct because a Virtual Router Identifier (VRID) is mandatory to identify the VRRP group; it is an integer (1–255) configured under the interface's vrrp-group stanza and must match across all routers participating in the same virtual router. Option C is wrong because VRRP is a first-hop redundancy protocol that operates independently of BGP, so no static BGP peering is needed. Option D is wrong because GRES (Graceful Routing Engine Switchover) is an optional high-availability feature for dual Routing Engines and is not a VRRP configuration requirement. Option E is wrong because VRRP can run on a physical interface or any logical interface and does not require an LACP aggregated Ethernet bundle.

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 14

Which THREE conditions can cause a Virtual Chassis primary Routing Engine election or switchover to occur unexpectedly? (Choose three)

Accepted Answer

Manual modification of member priority values followed by a mastership switchover command or reboot.. Option A is correct because Virtual Chassis primary RE election is influenced by the member priority value; changing priorities and then issuing a mastership switchover command or rebooting forces a new election that can unexpectedly move mastership. Option C is correct because Virtual Chassis relies on the stacking/VCP links for control and election communication; a cable failure or disconnection can split the fabric, trigger a new election, or cause topology restructuring that changes which member becomes primary. Option E is correct because a hardware crash or kernel panic on the current primary Routing Engine switch causes the backup RE to take over mastership, resulting in an unexpected switchover. Option B is not correct because VRRP preemption affects VRRP master election on a VLAN interface, not Virtual Chassis primary Routing Engine election. Option D is not correct because LACP timeout interval mismatches affect link aggregation behavior and can cause LACP bundling issues, but they do not directly trigger Virtual Chassis primary RE election or switchover.

Answer

Configuring VRRP preemption on a VLAN interface.

Answer

A mismatch in LACP timeout intervals on aggregated Ethernet interfaces.

Question 15

Which THREE parameters can be tuned under the VRRP hierarchy in Junos to customize failover timing and behavior? (Choose three)

Accepted Answer

Track interface priority decrement values to lower priority when upstream links fail.. Under the Junos VRRP hierarchy, option B is correct because the track interface configuration lets you specify a priority decrement (for example, track interface ge-0/0/0 priority-cost 30) so the router lowers its VRRP priority when a monitored upstream link fails, triggering a controlled failover. Option C is correct because the advertise-interval statement sets how often VRRP advertisement packets are sent (default 1 second), directly controlling failover detection timing. Option D is correct because the priority value (0–255, default 100) determines which router becomes master, with the higher priority winning and 255 triggering immediate preemption. Option A is not part of the VRRP hierarchy; LACP fast timeout is configured under aggregated Ethernet (lacp periodic fast) and concerns link-bundle heartbeats, not VRRP failover. Option E is also unrelated to VRRP; RE mastership priority is a Virtual Chassis setting (set virtual-chassis member 0 mastership-priority) for controlling Routing Engine roles, not VRRP master election.

Answer

LACP fast timeout timer to manage aggregated link heartbeats.

Answer

Routing engine mastership priority for Virtual Chassis roles.