CCNA High Availability Questions

Multi-Selecthard

Which THREE actions occur when a Junos router with GRES and NSR enabled performs a manual Routing Engine switchover while running OSPF and BGP? (Choose three)

Select 3 answers

A.OSPF and BGP daemon states synchronized via NSR allow routing sessions to remain established without neighbor drop.

B.External routing peers see no change in adjacency state and do not trigger route recalculations.

C.The backup Routing Engine assumes control plane mastership without resetting the packet forwarding engine.

D.All physical interfaces are reset and re-initialized, causing a 30-second traffic blackout.

E.All VRRP virtual gateway IPs revert to their physical interface fallback addresses.

AnswersA, B, C

NSR prevents protocol session drops by keeping protocol state synchronized on the backup RE.

Why this answer

Control plane state is preserved by NSR, forwarding continues uninterrupted via GRES, and external/internal neighbors do not detect adjacency drops.

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MCQhard

You are troubleshooting a Virtual Chassis formed by four EX4300 switches. The primary Routing Engine (RE) unexpectedly rebooted. Upon recovery, you notice that a different member switch has taken over the role of primary. How can you prevent this specific member from becoming the primary RE in the future?

A.Disable Graceful Routing Engine Switchover (GRES) on the backup routing engine.

B.Modify the routing-engine mastership-priority value on the preferred member switch to be higher than the others.

C.Enable preemption globally on all members in the virtual-chassis configuration.

D.Configure the non-preferred switch with a routing-engine user account restriction.

AnswerB

Configuring a higher priority value (up to 255) ensures that specific member is selected as primary.

Why this answer

Member priorities within a Junos Virtual Chassis determine which switch assumes the primary or backup role. Adjusting the virtual-chassis member priority ensures deterministic primary selection.

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Multi-Selecthard

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

Select 3 answers

A.Manual modification of member priority values followed by a mastership switchover command or reboot.

B.Configuring VRRP preemption on a VLAN interface.

C.Failure or disconnection of stacking cables resulting in a split-brain condition or topology restructuring.

D.A mismatch in LACP timeout intervals on aggregated Ethernet interfaces.

E.A hardware crash or kernel panic on the current primary Routing Engine switch.

AnswersA, C, E

Changing priorities alters the election outcome upon subsequent reboots or forced switches.

Why this answer

Stacking cable failures, primary RE hardware crashes, or manual mastership changes/priority modifications trigger switchovers.

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MCQmedium

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

A.Graceful Restart must be disabled globally on all routers.

B.VRRP must be configured on all BGP peering interfaces.

C.LACP fast mode must be enabled on all physical uplinks.

D.GRES must be enabled at the chassis level, and NSR must be explicitly enabled under the BGP protocol hierarchy.

AnswerD

NSR depends on chassis GRES for state synchronization and protocol-level configuration to replicate BGP daemon state to the backup RE.

Why this answer

NSR requires GRES enabled at the chassis level and NSR configured specifically under the routing-options protocols bfgp hierarchy.

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MCQhard

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?

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

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

C.Graceful Route Engine Switchover (GRES) and Nonstop Active Routing (NSR) must be enabled and functioning.

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

AnswerC

ISSU relies heavily on GRES and NSR to maintain routing states across the routing engine reboot during the upgrade process.

Why this answer

ISSU requires specific hardware compatibility (matching RE models, line card types), GRES and NSR configured and operating, and a supported Junos image path.

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MCQmedium

An engineer configures a Virtual Chassis using EX4300 switches. To ensure member IDs are assigned consistently even if physical positions change, how should the administrator provision the member IDs?

A.Rely on automatic plug-and-play assignment, which permanently locks member IDs based on initial boot order.

B.Disable GRES so that member IDs do not synchronize across the stack.

C.Configure the MAC address of each switch under the [edit chassis vrrp] hierarchy.

D.Pre-provision member serial numbers to specific member IDs using the 'request virtual-chassis assign' or configuration statements.

AnswerD

Pre-provisioning binds serial numbers to member IDs, ensuring consistent interface naming across reboots and hardware swaps.

Why this answer

Junos allows pre-provisioning Virtual Chassis member serial numbers to specific member IDs to maintain predictable topologies.

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MCQhard

You are troubleshooting a BGP session failure immediately following a manual Routing Engine switchover on an MX series router configured with GRES and NSR. BGP drops its peering session. What is the most likely reason for the failure?

A.NSR was not enabled under the BGP routing-options protocol hierarchy, causing the protocol daemon state to not synchronize to the backup Routing Engine.

B.The Virtual Chassis stacking cable was disconnected during the switchover.

C.VRRP preemption caused the default gateway IP to shift to the backup engine.

D.The LACP timeout on the aggregated uplink was set to slow mode.

AnswerA

While GRES preserves the forwarding plane, NSR must be explicitly enabled for specific protocols (like BGP or OSPF) to sync control plane states.

Why this answer

If NSR is enabled, protocol state is synced, but if Graceful Restart is misconfigured or helper mode is disabled on the peer, or if backup sync failed, state could be lost.

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MCQeasy

When configuring a Link Aggregation Group (LAG) on a Juniper switch, what is the naming convention used for the aggregated interface in the Junos CLI?

A.lag0, lag1, lag2, etc.

B.eth-trunk0, eth-trunk1, etc.

C.ae0, ae1, ae2, etc.

D.bond0, bond1, bond2, etc.

AnswerC

Aggregated Ethernet interfaces are designated with the 'ae' prefix followed by an integer index.

Why this answer

Junos uses the 'aeX' naming convention (Aggregated Ethernet) for LAG interfaces.

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MCQeasy

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

A.show lacp statistics

B.show vrrp summary

C.show virtual-chassis

D.show chassis hardware

AnswerC, D

show virtual-chassis displays the member ID, role, serial number, and status of each switch in the stack.

Why this answer

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

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MCQhard

You are performing a pre-check for an ISSU on an MX series router. You execute 'request system software in-service check' and the system reports an error indicating that graceful restart or NSR is not properly configured for active routing protocols. How do you resolve this?

A.Manually restart the routing protocol daemon (rpd) on both Routing Engines simultaneously.

B.Configure Nonstop Active Routing (NSR) or Graceful Restart for all active interior and exterior routing protocols before re-running the check.

C.Disable GRES to bypass protocol state verification checks.

D.Set the virtual-chassis mastership-priority to 255 on both routing engines.

AnswerB

ISSU requires routing protocols to be capable of surviving control plane restarts via NSR or Graceful Restart helper/restart mechanisms.

Why this answer

ISSU requires that either NSR or Graceful Restart is enabled for all running routing protocols to prevent loss of state during the control plane upgrade.

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MCQhard

You are troubleshooting a Virtual Chassis where member 0 has failed completely. The replacement switch arrives. Before inserting it into the running Virtual Chassis ring, what critical precaution must be taken regarding Junos OS software versions?

A.Ensure the replacement switch is running the exact same major and minor version of Junos OS as the existing Virtual Chassis master.

B.Disable LACP on all aggregated links across the stack.

C.Format the flash memory of the existing master switch before inserting the replacement.

D.Change the root password of the replacement switch to match the backup routing engine.

AnswerA

Junos Virtual Chassis requires identical software versions across all member switches to ensure compatible daemon communication and feature parity.

Why this answer

All member switches in a Junos Virtual Chassis must run the exact same version of Junos OS to prevent version mismatch errors and split-stack issues.

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MCQeasy

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?

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

B.To ensure uninterrupted data packet forwarding while the control plane routing protocol restarts.

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

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

AnswerB

Graceful Restart keeps forwarding tables populated using helper mode on neighbors while the control engine recovers.

Why this answer

Graceful Restart allows a routing platform to continue forwarding packets along known routes while its control plane is restarting, avoiding routing churn.

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MCQhard

You are troubleshooting a split-brain condition in an EX4300 Virtual Chassis where both partitions have elected a primary Routing Engine. Which feature can be configured to detect this condition and shut down downstream ports on the non-designated partition to prevent duplicate packet forwarding?

A.Setting LACP mode to active on the stacking ports.

B.Virtual Chassis split-detection or auxiliary management connection mechanisms that evaluate reachability between partitions to disable the non-primary partition.

C.Enabling GRES on both partitions simultaneously.

D.Configuring VRRP with a priority of 255 on all member interfaces.

AnswerB

Split-detection mechanisms or tie-breaker configurations prevent dual-primary states by shutting down interfaces on the isolated partition.

Why this answer

Dual-Routing Engine Advanced Support (DREAS) or specifically configured mechanisms like MAC-sec / split-detection scripts help, but let's look at Juniper's specific Virtual Chassis split-brain mitigation: Junos supports mechanisms such as MAC pinning or specifically configured split detection algorithms, or let's examine standard Juniper terminology. Wait, Junos Virtual Chassis uses Virtual Chassis Automatic Partition Detection or dedicated split-brain detection features. Let's see which option accurately names a valid approach.

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MCQmedium

An engineer wants to configure Nonstop Active Routing (NSR) alongside GRES on an MX204 router running OSPF. What is the primary operational benefit of enabling NSR compared to running GRES alone?

A.NSR automatically configures VRRP tracking on all local VLAN interfaces.

B.NSR allows software upgrades to be performed without ever rebooting either Routing Engine.

C.NSR synchronizes protocol daemon states between Routing Engines, preventing neighbors from detecting a control plane switchover.

D.NSR replaces LACP negotiation with static member pinning during link failures.

AnswerC

NSR keeps the backup RE fully synchronized with protocol states (like OSPF/BGP), so neighbors see zero disruption and no adjacency drops.

Why this answer

GRES preserves forwarding state during a switchover, but routing protocols must restart and re-converge unless NSR is running, which synchronizes routing protocol states between REs.

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MCQmedium

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?

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

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

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

D.The member interfaces must have matching speed, duplex, and LACP mode configuration.

AnswerD

All member links in an AE bundle must operate at identical speed and duplex settings, and share matching LACP active/passive modes.

Why this answer

LACP on Junos requires matching system priority, interface speeds, and duplex settings on both ends of the LAG, along with explicit configuration under the 'ae' interface.

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MCQmedium

An engineer configures VRRP between two routers. Client traffic destined for the outside network is being dropped intermittently. Investigation reveals that the VRRP master is responding to ARP requests with its physical MAC address instead of the virtual router MAC address. What is the cause of this behavior?

A.The virtual-mac-address option was explicitly disabled, or an incorrect configuration caused the master to use its physical interface MAC address for virtual IP ARP responses.

B.LACP fast mode was enabled on the VLAN interface.

C.GRES was disabled on the backup routing engine.

D.NSR was enabled without configuring BGP Graceful Restart.

AnswerA

Disabling virtual MAC addresses forces the master to answer ARP with its physical MAC, causing MAC table flapping on switches when mastership switches.

Why this answer

By default, VRRP routers respond to ARP requests with the virtual MAC address (00:00:5e:00:01:{VRID}), but certain misconfigurations or lack of virtual-mac-address support can cause issues. Wait, actually, standard Junos VRRP uses virtual MAC addresses. If virtual-mac-address is disabled or if proxy ARP / source NAT behaviors interfere, clients might get confused.

However, let's look at Junos specific VRRP behavior: Junos uses the standard virtual MAC address automatically. If ARP handling is normal, what causes physical MAC usage? In some platforms, if the virtual-mac-address is disabled or if tracking interacts incorrectly, or let's evaluate the options.

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MCQmedium

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?

A.Decrease the VRRP advertisement interval on the backup switch.

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

C.Disable the VRRP preempt feature on both routers.

D.Increase the VRRP priority value on the preferred switch's interface.

AnswerD

The router with the highest VRRP priority (default 100) becomes the master.

Why this answer

VRRP master selection is determined by priority. The router with the highest priority becomes the master. You can also configure track-interface commands to lower priority if link failures occur.

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MCQeasy

An administrator wants to verify that GRES is operating correctly on an MX series router with dual Routing Engines. Which operational command should be used?

A.show system backup-router

B.show virtual-chassis gres

C.show chassis routing-engine

D.show gres statistics

AnswerC

This command displays master/backup status, CPU, memory, and whether GRES is enabled and synchronized.

Why this answer

The command 'show chassis routing-engine' shows the status of both routing engines, their synchronization state, and GRES status.

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Multi-Selectmedium

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

Select 3 answers

A.Both Routing Engines must be fully populated with identical hardware models and supported Junos images.

B.Graceful Routing Engine Switchover (GRES) must be enabled and synchronized.

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

D.VRRP preemption must be disabled on all routing interfaces.

E.Nonstop Active Routing (NSR) or Graceful Restart must be configured for active routing protocols.

AnswersA, B, E

Compatible hardware and software paths are required for a successful ISSU.

Why this answer

ISSU requires GRES enabled, NSR or graceful restart configured, and matching hardware/software paths.

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MCQeasy

Which CLI command is used to manually initiate a Routing Engine switchover on an MX series router configured with GRES?

A.restart routing-engine backup

B.request chassis routing-engine master switch

C.request system reboot backup

D.set chassis routing-engine switchover

AnswerB

This command triggers a controlled switchover to test or invoke GRES.

Why this answer

The 'request chassis routing-engine master switch' command forces a manual switchover from the primary to the backup Routing Engine.

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MCQeasy

Which CLI command displays detailed information about VRRP groups, including master router status, virtual IP addresses, and advertisement intervals on an EX series switch?

A.show lacp vrrp-status

B.show vrrp detail

C.show spanning-tree vrrp

D.show chassis vrrp

AnswerB

show vrrp detail provides comprehensive output including master state, priority, timers, and tracking status.

Why this answer

The 'show vrrp interface' or 'show vrrp detail' commands provide granular details regarding VRRP instance status.

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MCQmedium

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?

A.The tracking decrement value set to zero.

B.The preemption parameter (enabled by default), which allows a higher-priority router to preempt the current master.

C.The virtual-mac-address configuration statement.

D.The advertisement interval timer set to 1 millisecond.

AnswerB

Preemption ensures that the highest priority router automatically reclaims mastership upon recovery.

Why this answer

Preemption is enabled by default in Junos VRRP, allowing a higher-priority router to take over when it comes back online.

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MCQmedium

An EX4300 Virtual Chassis has GRES enabled. During a primary Routing Engine failure, what happens to the backup Routing Engine?

A.The backup Routing Engine reboots both engines to synchronize firmware versions.

B.The Virtual Chassis splits into independent standalone switches.

C.The backup Routing Engine assumes the primary role without disrupting the forwarding plane or resetting packet forwarding tables.

D.All switch members in the Virtual Chassis are forced into factory default mode.

AnswerC

GRES ensures smooth transition of control plane mastership while keeping the Packet Forwarding Engine (PFE) running uninterrupted.

Why this answer

With GRES enabled, the backup Routing Engine assumes the primary role seamlessly without resetting the forwarding plane or dropping data traffic.

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Multi-Selecthard

Which THREE statements regarding Juniper Virtual Chassis architecture and master election are correct? (Choose three)

Select 3 answers

A.Pre-provisioning member serial numbers ensures consistent member ID assignments regardless of boot order.

B.Split-brain detection automatically shuts down all core routing protocols without administrator intervention.

C.If the primary Routing Engine fails, the backup member assumes the primary role seamlessly if GRES is active.

D.Virtual Chassis ports (VCPs) require LACP active mode configuration on every stacking cable.

E.Mastership priority values range from 0 to 255, with the highest value preferred for the primary role.

AnswersA, C, E

Serial number binding prevents ID shifts when hardware is swapped or rebooted.

Why this answer

Virtual Chassis mastership is determined by priority, preemption can cause takeovers, and pre-provisioning serial numbers ensures stable member IDs.

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MCQeasy

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

A.show chassis vcp

B.show lacp virtual-chassis

C.show virtual-chassis

D.show vrrp chassis

AnswerC

show virtual-chassis is the primary command for checking Virtual Chassis membership and roles.

Why this answer

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

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MCQeasy

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?

A.show interfaces ae0 statistics

B.show chassis lacp-status

C.show vrrp lacp-summary

D.show lacp interface

AnswerD

show lacp interface lists each member link, its partner system ID, partner port ID, and active aggregation status.

Why this answer

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

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MCQmedium

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?

A.Each partition elects its own primary routing engine if dual primary detection is not enabled, leading to potential duplicate IP scenarios.

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

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

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

AnswerA

Without explicit split-brain mitigation or adequate mastership conflict handling, separated partitions may both attempt to operate as primary.

Why this answer

Without auxiliary diagnostic mechanisms like Dual-Routing Engine Advanced Support (DREAS) or specifically configured split-brain detection, a split Virtual Chassis can result in duplicate primary assignments unless properly managed with master conflict resolution behaviors.

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Multi-Selecthard

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

Select 3 answers

A.If the decremented priority falls below the backup router's priority, mastership transitions to the backup router.

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

C.Multiple interfaces or reachability paths can be monitored simultaneously within a single VRRP tracking configuration.

D.Tracking automatically disables GRES on the routing engine.

E.Tracking allows a router to automatically decrement its VRRP priority when a monitored interface goes down.

AnswersA, C, E

Priority changes drive the master election when tracking triggers a penalty.

Why this answer

VRRP tracking lowers priority when interfaces fail, can monitor multiple interfaces, and allows backup routers to take over.

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MCQeasy

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

A.An IP address belonging to the same subnet as the physical interface connected to the broadcast domain.

B.A loopback IP address configured on the master Routing Engine.

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

D.A reserved multicast address in the 224.0.0.18 range.

AnswerA

Clients in the broadcast domain use this virtual IP address as their default gateway, requiring it to be in their local subnet.

Why this answer

The virtual IP address must belong to the same subnet as the physical interface IP address configured on the participating routers.

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Multi-Selectmedium

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

Select 3 answers

A.LACP fast timeout timer to manage aggregated link heartbeats.

B.Track interface priority decrement values to lower priority when upstream links fail.

C.Advertisement interval to control how frequently VRRP heartbeat packets are transmitted.

D.Priority value to determine which router becomes the master.

E.Routing engine mastership priority for Virtual Chassis roles.

AnswersB, C, D

Tracking drops priority dynamically upon link failure.

Why this answer

VRRP parameters include priority, advertisement interval, and tracking penalties/decrement values.

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MCQhard

When planning an In-Service Software Upgrade (ISSU) on a Juniper routing platform, what is the behavior of the Routing Engines during the execution of the upgrade command?

A.Both Routing Engines are rebooted simultaneously, relying entirely on OSPF Graceful Restart helper mode.

B.The forwarding plane is restarted first, followed by a simultaneous upgrade of the dual REs.

C.The primary Routing Engine is wiped and reloaded while data traffic is redirected through the console port.

D.The backup Routing Engine is upgraded, a graceful switchover takes place, and then the newly elected backup Routing Engine is upgraded.

AnswerD

ISSU upgrades the backup RE, performs a GRES switchover, and then upgrades the second RE, all while data forwarding continues.

Why this answer

During ISSU, the backup RE is upgraded first, then a switchover occurs, and then the former primary RE is upgraded, maintaining control plane availability.

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MCQhard

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?

A.Confirm that LACP minimum-links is set to zero.

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

C.Verify that all external BGP peers negotiated Graceful Restart capability and that helper mode was active on both ends prior to initiating the upgrade.

D.Ensure VRRP preemption is turned off on all core interfaces.

AnswerC

If peers do not support or have graceful restart enabled as helpers, they will drop the BGP session when the control plane restarts during ISSU.

Why this answer

Verifying that BGP graceful restart and helper modes were fully operational and peer routers had acknowledged the capability before starting ISSU.

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Multi-Selecteasy

Which TWO operational commands are used to check the health and status of Routing Engines and GRES on an MX series router? (Choose two)

Select 2 answers

A.show chassis routing-engine

B.show vrrp summary

C.show lacp statistics

D.show chassis alarms

E.show virtual-chassis

AnswersA, D

Displays RE status, master/backup roles, CPU/memory usage, and GRES synchronization.

Why this answer

Administrators use 'show chassis routing-engine' and 'show system alarms' or similar chassis commands.

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MCQhard

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?

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

B.Review interface error counters, ensure physical link stability, and increase the VRRP advertisement interval if transient congestion is dropping packets.

C.Disable Virtual Chassis on both switches.

D.Remove GRES from the routing engine configuration.

AnswerB

Stabilizing physical links and tuning advertisement intervals prevents backup routers from assuming the master role due to missed heartbeat advertisements.

Why this answer

Frequent mastership flipping (flapping) is typically caused by missing advertisements due to interface drops, high CPU, or mismatched timers. Increasing advertisement intervals or tuning timers resolves this.

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Multi-Selecteasy

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

Select 2 answers

A.At least one virtual IP address configured to act as the default gateway for clients.

B.A Virtual Router Identifier (VRID) integer.

C.A static BGP peering session to an upstream provider.

D.A pre-configured GRES license on the Routing Engine.

E.An active LACP aggregated Ethernet bundle.

AnswersA, B

Clients use the virtual IP as their gateway address.

Why this answer

VRRP configuration requires a Virtual Router ID (VRID) and at least one virtual IP address.

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MCQhard

You are troubleshooting a Link Aggregation Group (LAG) between an EX4300 switch and a third-party switch. Member links are flapping intermittently. Examination of system logs reveals LACP timeout errors. What is the most likely cause?

A.The Virtual Chassis primary routing engine priority is set too low.

B.VRRP preemption is enabled on the aggregated interface.

C.GRES is disabled on the EX4300 switch.

D.A mismatch in LACP timeout settings (e.g., one side configured for fast timeout while the other sends slow intervals) causing dropped sessions.

AnswerD

Mismatched LACP timeouts frequently result in one end timing out and dropping the link bundle member.

Why this answer

LACP timeouts occur when LACP data units (LACPDUs) are not received within the negotiated timeout window (typically 3 seconds for fast, 90 seconds for slow).

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Multi-Selectmedium

Which THREE criteria are evaluated by Junos when electing the primary Routing Engine in an EX Series Virtual Chassis? (Choose three)

Select 3 answers

A.Switch uptime or boot order sequence if priorities are identical.

B.The VRRP router ID configured on VLAN 1.

C.Base MAC address of the switch as a deterministic tie-breaker.

D.Configured routing-engine mastership priority values.

E.The number of active LACP links connected to member 0.

AnswersA, C, D

Boottime/uptime acts as a tie-breaker when priorities match.

Why this answer

Virtual Chassis master election evaluates pre-configured priority, uptime/boot order, and lowest MAC address as tie-breakers.

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MCQmedium

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?

A.Configure 'set interfaces ae0 aggregated-ether-options lacp minimum-links 2'.

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

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

D.Configure 'set switch-options lacp threshold 2'.

AnswerA

The 'minimum-links' parameter ensures the aggregate interface goes down if active member count falls below the specified threshold.

Why this answer

Junos allows setting a minimum number of active links for an aggregated interface using the 'minimum-links' command.

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MCQhard

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?

A.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.

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

C.Disable LACP on all aggregated links across the stack.

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

AnswerA

Matching the Junos OS version offline before adding the switch to the VC ring prevents software incompatibility errors.

Why this answer

To recover from a version/hardware mismatch when adding a new switch to an existing Virtual Chassis, you must update the new switch's software to match the existing VC before cabling it into the stack.

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MCQmedium

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?

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

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

C.The switch initiates an immediate In-Service Software Upgrade.

D.The VRRP priority is decremented by a configured value so that the backup router can assume the master role.

AnswerD

Priority decrementing ensures that a router experiencing an upstream uplink failure relinquishes its VRRP mastership.

Why this answer

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.

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Multi-Selecteasy

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

Select 2 answers

A.Increased aggregate bandwidth between connected networking devices.

B.Synchronization of BGP routing daemon state between separate routers.

C.Automatic upgrade of Junos OS across peer devices.

D.Redundancy and automatic failover if a physical member link fails.

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

AnswersA, D

Combining multiple physical links pools their bandwidth into a single logical pipe.

Why this answer

LAGs provide increased aggregate bandwidth and link redundancy/failover.

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MCQeasy

Which CLI command verifies that OSPF Graceful Restart helper mode is enabled by default on a Juniper routing platform?

A.show chassis ospf-status

B.show lacp ospf-helper

C.show ospf overview

D.show vrrp ospf-restart

AnswerC

show ospf overview shows global OSPF parameters, including whether graceful restart helper is enabled.

Why this answer

Running 'show ospf neighbor detail' or 'show ospf overview' displays protocol-level graceful restart helper status.

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MCQhard

You are configuring Multi-Chassis Link Aggregation (MC-LAG) across two Juniper switches acting as separate control plane devices. Which protocol is used between the peer switches to synchronize state and ensure MAC address table consistency across the MC-LAG domain?

A.Open Shortest Path First (OSPF)

B.Graceful Routing Engine Switchover (GRES)

C.Inter-Chassis Control Protocol (ICCP)

D.Virtual Router Redundancy Protocol (VRRP)

AnswerC

ICCP runs over an inter-chassis link (ICL) between MC-LAG peers to exchange control and status messages.

Why this answer

MC-LAG uses Inter-Chassis Control Protocol (ICCP) to coordinate state, consistency, and status between the two peer switches.

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MCQhard

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?

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

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

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

D.Virtual Chassis ports (VCPs) must be explicitly configured to match supported transceiver speeds, and mixing unsupported interface types will result in port initialization failure.

AnswerD

Junos enforces strict hardware compliance for VCP connections; mismatched or unsupported transceiver types will fail to form a valid VC ring/chain.

Why this answer

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.

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MCQeasy

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

A.show lacp aggregated-devices

B.show virtual-chassis

C.show chassis alarms

D.show vrrp mastership

AnswerB

show virtual-chassis provides the complete status table for all switches in the Virtual Chassis.

Why this answer

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

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MCQeasy

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

A.set routing-options gres enable

B.set interfaces redundancy gres

C.set chassis redundancy graceful-switchover

D.set system graceful-restart

AnswerC

This command enables GRES on the chassis, allowing control plane state synchronization to support seamless routing engine failovers.

Why this answer

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

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MCQmedium

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?

A.Omit the LACP protocol configuration under the aggregated-ether-options stanza, operating in static mode.

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

C.Configure LACP passive mode on the EX4300 switch.

D.Enable Graceful Restart on the physical ports.

AnswerA

Without LACP enabled under aggregated-ether-options, the interface operates as a static, non-LACP LAG.

Why this answer

When connecting to a device that does not support LACP, you must configure the Junos aggregated interface without LACP (manual/static mode).

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MCQmedium

You notice frequent mastership transitions in a VRRP group configured between two EX4300 switches. The logs indicate that VRRP advertisements are intermittently missing. Which troubleshooting step addresses the underlying cause without changing the master priority?

A.Disable Virtual Chassis on both switches to allow VRRP to function properly.

B.Check physical interface error counters and increase the VRRP advertisement interval if packet drops occur.

C.Remove LACP from all aggregated interfaces connected to the VRRP routers.

D.Configure Nonstop Active Routing (NSR) under the VRRP hierarchy.

AnswerB

Increasing the advertisement interval or checking interface error counters helps accommodate transient network congestion or drops.

Why this answer

Missing advertisements are often caused by packet loss or excessive CPU load on the master. Tuning timers or checking interface drops/queues resolves this.

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Multi-Selecteasy

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

Select 2 answers

A.show virtual-chassis

B.show vrrp detail

C.show interfaces ae0

D.show lacp interface

E.show chassis routing-engine

AnswersC, D

Displays traffic statistics, error counts, and operational status of the aggregated interface.

Why this answer

To verify LACP and LAG status, administrators use 'show lacp interface' and 'show interfaces ae0'.

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MCQeasy

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

A.The interface will actively transmit LACP packets to initiate and negotiate the aggregation with the peer device.

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

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

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

AnswerA

Active mode means the port initiates LACP negotiations. Passive mode waits for the peer to initiate.

Why this answer

In LACP active mode, the interface actively transmits LACP packets to the remote peer to negotiate the link aggregation.

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MCQeasy

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

A.show interfaces ae0

B.show chassis interface-drops ae0

C.show virtual-chassis interface ae0

D.show lacp statistics ae0

AnswerA

This command displays traffic totals, input/output packet counts, errors, and physical link states for the aggregated interface.

Why this answer

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

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Multi-Selecthard

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

Select 3 answers

A.Traffic loops may occur if static LAG mode is mismatched with LACP active mode on opposite ends.

B.The aggregated interface may go operationally down if active member links drop below the configured minimum-links threshold.

C.GRES will be disabled on the routing engine automatically.

D.Member links may be placed in 'Suspended' or 'Expired' states if LACP protocol handshakes fail.

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

AnswersA, B, D

Mismatched static vs dynamic LACP configurations can disrupt bundle formation and cause forwarding anomalies.

Why this answer

LACP misconfigurations can lead to link suspension, flapping due to timeout mismatches, or bundle failure if minimum links aren't met.

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Multi-Selectmedium

Which THREE factors must be considered when configuring a Link Aggregation Group (LAG) with LACP on Junos switches? (Choose three)

Select 3 answers

A.A minimum number of active links can be configured to ensure traffic drops if bandwidth falls below a threshold.

B.VRRP must be enabled on every member port for LACP to negotiate successfully.

C.All member links must have identical speed, duplex, and LACP active/passive settings.

D.Aggregated device counts must be defined under the [edit chassis aggregated-devices ethernet] hierarchy.

E.GRES must be enabled on all switches participating in a LAG.

AnswersA, C, D

The 'minimum-links' option drops the aggregated interface if active member count is too low.

Why this answer

LAG configuration requires matching speed/duplex, proper device-count definition under chassis, and matching LACP modes.

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MCQhard

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?

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

B.Run 'show bgp neighbor' and verify that the 'Graceful Restart' capability is advertised and received, and observe the restart state flags.

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

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

AnswerB

BGP summary and neighbor detail outputs show negotiated GR capabilities and active helper timers.

Why this answer

Using 'show bgp neighbor' displays the graceful restart capabilities negotiated and whether the peer is currently in restart state.

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MCQmedium

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?

A.The Virtual Chassis primary routing engine license has expired.

B.The Junos software license for aggregated Ethernet has expired.

C.The GRES synchronization timer has timed out.

D.The local port has stopped receiving LACP packets from the remote peer within the timeout window.

AnswerD

Expired state indicates communication failure with the peer switch regarding LACP heartbeats.

Why this answer

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

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Multi-Selecteasy

Which TWO methods are used to connect switches in a Juniper EX Series Virtual Chassis? (Choose two)

Select 2 answers

A.Dedicated Virtual Chassis ports (VCPs) using specialized stacking cables.

B.Using standard serial console rollover cables for data and stacking traffic.

C.Configuring standard network uplink ports (such as 10G/40G interfaces) to operate as Virtual Chassis ports.

D.Running LACP over independent fiber strands between standalone switches.

E.Connecting standard access ports using unmanaged layer 2 Ethernet hubs.

AnswersA, C

Dedicated VCP ports provide high-speed ring/chain connectivity between members.

Why this answer

EX Series switches use dedicated Virtual Chassis ports (VCPs) or uplink modules configured as VCPs using specialized cables.

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MCQmedium

An engineer wants to configure a Link Aggregation Group (LAG) to load-balance traffic based on Layer 3 and Layer 4 header fields (source/destination IP and source/destination port) rather than just Layer 2 MAC addresses. How is this achieved in Junos?

A.Configure load-balance profiles under [edit forwarding-options hash-key] specifying inet protocols.

B.Enable LACP multi-chassis hashing under the chassis hierarchy.

C.Configure 'set interfaces ae0 load-balance layer-3-4' directly under the interface stanza.

D.Set the LACP periodic transmission interval to fast.

AnswerA

Configuring hash keys under forwarding-options allows granular control over how LAG and ECMP hash traffic across member links.

Why this answer

Junos allows configuring load-balancing profiles under the forwarding-options hierarchical level to include IP and port hash fields.

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Multi-Selectmedium

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

Select 3 answers

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

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

C.It helps prevent unnecessary SPF recalculations across the network during transient control plane restarts.

D.Helper mode enables a router to assist a restarting neighbor by maintaining its routing entries during the restart window.

E.Helper mode is enabled by default for OSPF in Junos OS.

AnswersC, D, E

Suppressing adjacency drops avoids network-wide routing churn.

Why this answer

Helper mode allows routers to maintain routing tables while neighbors restart, suppressing routing churn and dropping adjacencies prematurely.

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