JNCIS-ENT High Availability Practice Test 3 — 15 Questions

Question 1

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?

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

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 2

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?

Accepted Answer

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.. 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.

Answer

LACP fast mode was enabled on the VLAN interface.

Answer

GRES was disabled on the backup routing engine.

Answer

NSR was enabled without configuring BGP Graceful Restart.

Question 3

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?

Accepted Answer

Configure load-balance profiles under [edit forwarding-options hash-key] specifying inet protocols.. Junos allows configuring load-balancing profiles under the forwarding-options hierarchical level to include IP and port hash fields.

Answer

Enable LACP multi-chassis hashing under the chassis hierarchy.

Answer

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

Answer

Set the LACP periodic transmission interval to fast.

Question 4

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?

Accepted Answer

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

Answer

Setting LACP mode to active on the stacking ports.

Answer

Enabling GRES on both partitions simultaneously.

Answer

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

Question 5

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?

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 6

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 7

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.. 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.

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 8

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 9

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 10

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 11

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 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.

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 12

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 13

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 14

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

Answer

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

Answer

Tracking automatically disables GRES on the routing engine.

Question 15

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

Accepted Answer

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

Answer

show virtual-chassis

Answer

show vrrp detail

Answer

show chassis routing-engine