JNCIS-ENT High Availability Practice Test 2 — 15 Questions

Question 1

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.. Option C is correct because OSPF Graceful Restart helper mode keeps the adjacency and LSDB state stable while a neighbor restarts its control plane, so other routers do not trigger unnecessary SPF recalculations and network-wide churn during the transient outage. Option D is correct because the helper router continues to advertise and retain the restarting neighbor's routing entries (treating the neighbor as still reachable) for the duration of the restart window, preserving forwarding while the control plane recovers. Option E is correct because in Junos OS, OSPF graceful restart helper mode is enabled by default, so a Juniper router will assist a restarting OSPF neighbor without requiring explicit helper configuration. Option A is incorrect because graceful restart is specifically designed to preserve data forwarding during the control plane restart, not to drop forwarding traffic immediately. Option B is incorrect because VRRP tracking on loopback interfaces is unrelated to OSPF graceful restart helper operation and is not a requirement for it.

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 2

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.. Option A is correct because if one side is configured as a static LAG (no LACP) and the other side runs LACP active, the peer will not form a proper bundle and the resulting forwarding inconsistency can create traffic loops, especially with multiple links. Option B is correct because a LAG configured with a minimum-links threshold will bring the aggregate interface operationally down when the number of active member links falls below that threshold, which is a direct consequence of misconfigured or failed LACP negotiation. Option D is correct because when LACP protocol data units (PDUs) are not exchanged successfully, member links can enter 'Suspended' or 'Expired' states in the LACP state machine, preventing them from being used in the bundle. Option C is not correct because GRES (Graceful Routing Engine Switchover) is a high-availability feature independent of LACP and is not automatically disabled by an LACP mismatch. Option E is not correct because ISSU is a manual, administrator-initiated upgrade procedure and is never triggered automatically by an LACP configuration mismatch.

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 3

You administer a pair of Juniper EX4600 switches configured as a Virtual Chassis with two routing engines in a mixed mode (one master, one backup). You want to ensure that the backup routing engine is ready to take over immediately if the master fails, without requiring a full reboot. Which statement correctly describes the default behavior of the Virtual Chassis when the master Routing Engine fails?

Accepted Answer

The backup Routing Engine becomes master and maintains the forwarding state of the line cards, provided that graceful switchover is enabled.. Graceful switchover allows the backup Routing Engine to assume the master role without resetting the line cards, preserving forwarding state and minimizing traffic disruption. This is critical for high availability in a Virtual Chassis. Without graceful switchover, a failover might cause line card resets and longer outages.

Answer

The master Routing Engine must be manually failed over using the request chassis routing-engine master switch command before the backup can take over.

Answer

The backup Routing Engine automatically becomes master and the line cards are reset, causing a brief traffic disruption.

Answer

The backup Routing Engine reboots and then assumes the master role, causing a longer outage.

Question 4

You are configuring a Juniper EX4300 switch in a Virtual Chassis with two members. You want to enable graceful Routing Engine switchover (GRES) and ensure that the backup Routing Engine is synchronized with the master for kernel and forwarding state. Which additional configuration is required to achieve this synchronization?

Accepted Answer

Enable graceful-switchover under the [edit chassis redundancy] hierarchy.. Graceful Routing Engine switchover (GRES) is enabled by configuring the graceful-switchover statement under the [edit chassis redundancy] hierarchy. This allows the backup Routing Engine to synchronize kernel and forwarding state with the master, enabling a seamless takeover. Without this configuration, the backup cannot maintain synchronization.

Answer

Configure Nonstop Active Routing (NSR) under the [edit routing-options] hierarchy.

Answer

Enable VRRP on all interfaces to synchronize state between Routing Engines.

Answer

Configure the backup Routing Engine to be the master using the request chassis routing-engine master switch command.

Question 5

You are deploying a new EX4300 Virtual Chassis with four members. You want to ensure that the control plane remains available if the master Routing Engine fails. Which TWO actions should you perform? (Choose two.)

Accepted Answer

Configure a backup member by setting the mastership priority appropriately on at least one other member.. Control-plane redundancy in a Virtual Chassis requires a backup member that is ready to assume the master role. This is achieved by configuring mastership priorities so that at least one other member becomes the backup, and by ensuring that member is properly connected through Virtual Chassis ports. Together, these actions ensure the backup can take over if the master fails.

Answer

Set the master member's mastership priority to the highest possible value.

Answer

Configure Nonstop Active Routing (NSR) on all members.

Answer

Enable graceful Routing Engine switchover (GRES) on the Virtual Chassis.

Question 6

You are configuring a VRRP group on an EX4300 switch. The master router has a priority of 150, and the backup has a priority of 100. You want the backup to take over if the master fails, but you also want the master to resume its role when it comes back online. Which VRRP setting should you enable on the backup?

Accepted Answer

Preempt. Preempt is the VRRP feature that allows a backup to yield the master role to a router with a higher priority when that router becomes available. In this scenario, the original master has priority 150, which is higher than the backup's 100. Enabling preempt on the backup ensures that when the original master returns, it will reclaim the master role.

Answer

A shorter advertisement interval

Answer

Authentication

Answer

Interface tracking

Question 7

You are troubleshooting a VRRP configuration on an EX4300 switch. The master router is not sending VRRP advertisements, and the backup router has become master. You check the configuration and see that the master's VRRP interface is up and has the correct IP address. Which command would you use to verify the VRRP state and advertisement status on the master?

Accepted Answer

show vrrp. The show vrrp command is the standard operational command to display VRRP state, including which router is master, the priority, and the advertisement interval. It also indicates whether the local router is sending advertisements. This information is essential to determine why the backup has taken over, such as the master not sending advertisements or being in a non-master state.

Answer

show vrrp summary

Answer

show vrrp extensive

Answer

show vrrp detail

Question 8

An engineer is preparing to perform an In-Service Software Upgrade (ISSU) on a pair of dual-RE MX240 routers. Which condition must be met to ensure the ISSU succeeds without dropping traffic?

Accepted Answer

Graceful Route Engine Switchover (GRES) and Nonstop Active Routing (NSR) must be enabled and functioning.. ISSU requires specific hardware compatibility (matching RE models, line card types), GRES and NSR configured and operating, and a supported Junos image path.

Answer

The backup Routing Engine must be physically removed from the chassis during the upgrade.

Answer

All physical interfaces must be manually disabled prior to issuing the request system software in-service command.

Answer

All routing protocols must be migrated from OSPF to IS-IS before starting ISSU.

Question 9

You are configuring VRRP between two EX4600 switches to provide a default gateway for a VLAN. To ensure that the switch with the higher physical interface capacity assumes the master role, what parameter should you adjust?

Accepted Answer

Increase the VRRP priority value on the preferred switch's interface.. VRRP elects the master based on the highest priority value (default 100, range 1–254, with 255 reserved for the address owner). To ensure the switch with greater capacity becomes master, you increase its VRRP priority above the other switch's. The master then owns the virtual IP and forwards traffic for the VLAN, while the backup monitors advertisements and takes over if the master fails.

Answer

Decrease the VRRP advertisement interval on the backup switch.

Answer

Set the virtual router identifier (VRID) to a lower integer value on the preferred switch.

Answer

Disable the VRRP preempt feature on both routers.

Question 10

An EX4300 Virtual Chassis experiences a split-brain condition due to a failure of all stacking cables between members 0/1 and members 2/3. How does Junos handle this scenario by default?

Accepted Answer

Each partition elects its own primary routing engine if dual primary detection is not enabled, leading to potential duplicate IP scenarios.. By default, when a Virtual Chassis splits into two partitions due to stacking cable failure, each partition elects its own primary Routing Engine if dual primary detection is not enabled. This leads to two active primaries, causing potential duplicate IP addresses and network instability. Junos does not automatically shut down interfaces or reboot the entire VC.

Answer

All member switches across both partitions automatically shut down all data interfaces to prevent loops.

Answer

The backup routing engine instantly shuts down its control plane daemon permanently.

Answer

The entire Virtual Chassis reboots simultaneously until stacking cables are re-seated.

Question 11

An administrator is configuring Graceful Restart on a pair of Juniper MX series routers running OSPF. What is the primary purpose of Graceful Restart in this scenario?

Accepted Answer

To ensure uninterrupted data packet forwarding while the control plane routing protocol restarts.. Graceful Restart (GR) in OSPF allows a router to restart its control plane (routing protocol process) while the forwarding plane continues to forward packets uninterrupted. The router signals its neighbors that it is restarting, and they continue to advertise the restarting router's links as if it were still up, preventing a full SPF recalculation and traffic loss. This ensures uninterrupted data forwarding during the restart.

Answer

To instantly drop all adjacencies and force an immediate full SPF recalculation across the network.

Answer

To automatically upgrade Junos OS images without rebooting the forwarding plane.

Answer

To synchronize firewall filter counters between primary and backup Routing Engines.

Question 12

You are verifying BGP Graceful Restart helper mode on a Juniper router. A peering router restarts its control plane. What output or verification command confirms that your router is acting as a Graceful Restart helper for the peer?

Accepted Answer

Run 'show bgp neighbor' and verify that the 'Graceful Restart' capability is advertised and received, and observe the restart state flags.. Using 'show bgp neighbor' displays the graceful restart capabilities negotiated and whether the peer is currently in restart state.

Answer

Run 'show chassis routing-engine' to verify that the remote neighbor has updated its local RE priority.

Answer

Run 'show lacp statistics ae0' to see if LACP packets are being suppressed during restart.

Answer

Run 'show vrrp summary' to check if the BGP neighbor has assumed the master VRRP role.

Question 13

You are configuring a Link Aggregation Group (LAG) on an EX series switch. Which statement is correct regarding LACP active mode?

Accepted Answer

The interface will actively transmit LACP packets to initiate and negotiate the aggregation with the peer device.. In LACP active mode, the interface actively transmits LACP packets to the remote peer to negotiate the link aggregation.

Answer

The interface will only respond to LACP packets and never transmit them.

Answer

Active mode can only be used when connecting Juniper switches to non-Juniper servers.

Answer

LACP active mode requires static pinning of member links and disables dynamic hash selection.

Question 14

An engineer needs to configure a Link Aggregation Group (LAG) between two Juniper EX4300 switches to provide redundant uplinks to a core router. Which statements regarding the LACP configuration requirements on the EX4300 switch must be met?

Accepted Answer

The member interfaces must have matching speed, duplex, and LACP mode configuration.. On Juniper EX switches, all physical member links of an aggregated Ethernet (ae) interface must be configured identically in terms of speed, duplex, and LACP mode (active/passive) for the bundle to come up. If any member link negotiates a different speed/duplex or is placed in a mismatched LACP mode, that link is excluded from the LAG and may remain in a down or standby state. This consistency requirement ensures the LACP state machine can form a single logical link with a stable operational key across all member ports.

Answer

LAG interfaces do not require explicit definition under the chassis stanza.

Answer

LACP multi-chassis mode must be enabled for a single switch LAG.

Answer

LACP heartbeat intervals are strictly hardcoded to 1 second and cannot be modified.

Question 15

You are configuring a Link Aggregation Group (LAG) with LACP on an EX3400 switch. You want to ensure that the interface bundle drops traffic if fewer than two active member links are operational. Which feature configuration achieves this?

Accepted Answer

Configure 'set interfaces ae0 aggregated-ether-options lacp minimum-links 2'.. On Junos EX switches, the LACP minimum-links feature is configured under the aggregated Ethernet interface using 'set interfaces ae0 aggregated-ether-options lacp minimum-links 2'. This setting ensures that if fewer than two member links are active, the LAG is marked down and traffic is dropped, preventing degraded forwarding.

Answer

Configure 'set protocols lacp minimum-active-ports 2'.

Answer

Configure 'set chassis aggregated-devices ethernet link-threshold 2'.

Answer

Configure 'set switch-options lacp threshold 2'.