JNCIS-ENT High Availability — 30 Questions

Question 1

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 2

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 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.

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 3

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.. 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.

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 4

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

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 5

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?

Accepted Answer

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

Answer

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

Answer

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

Answer

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

Question 6

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 7

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 8

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.. 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.

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 9

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

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'.

Question 10

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?

Accepted Answer

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

Answer

show system backup-router

Answer

show virtual-chassis gres

Answer

show gres statistics

Question 11

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?

Accepted Answer

The backup Routing Engine is upgraded, a graceful switchover takes place, and then the newly elected backup Routing Engine is upgraded.. During ISSU, the backup RE is upgraded first, then a switchover occurs, and then the former primary RE is upgraded, maintaining control plane availability.

Answer

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

Answer

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

Answer

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

Question 12

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?

Accepted Answer

Check physical interface error counters and increase the VRRP advertisement interval if packet drops occur.. Missing advertisements are often caused by packet loss or excessive CPU load on the master. Tuning timers or checking interface drops/queues resolves this.

Answer

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

Answer

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

Answer

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

Question 13

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 14

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 15

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 16

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?

Accepted Answer

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

Answer

NSR automatically configures VRRP tracking on all local VLAN interfaces.

Answer

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

Answer

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

Question 17

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

Accepted Answer

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

Answer

show lacp vrrp-status

Answer

show spanning-tree vrrp

Answer

show chassis vrrp

Question 18

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?

Accepted Answer

Pre-provision member serial numbers to specific member IDs using the 'request virtual-chassis assign' or configuration statements.. Junos allows pre-provisioning Virtual Chassis member serial numbers to specific member IDs to maintain predictable topologies.

Answer

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

Answer

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

Answer

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

Question 19

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?

Accepted Answer

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

Answer

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

Answer

VRRP preemption is enabled on the aggregated interface.

Answer

GRES is disabled on the EX4300 switch.

Question 20

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?

Accepted Answer

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

Answer

The Virtual Chassis stacking cable was disconnected during the switchover.

Answer

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

Answer

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