JNCIS-ENT High Availability Practice Test 3 — 15 Questions

Question 1

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 an In-Service Software Upgrade (ISSU) on Juniper routing platforms, the process upgrades the backup Routing Engine first, then performs a graceful switchover to make it the primary, and finally upgrades the new backup (formerly primary) Routing Engine. This ensures that at least one RE is always available to maintain control plane operations and forwarding, minimizing downtime.

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 2

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 3

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 4

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 5

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 timeout errors and flapping member links are typically caused by a mismatch in LACP timeout configuration between the two sides. If one side uses fast (short) timeout and the other sends slow (long) intervals, the fast side may declare the LACPDU timeout and drop the session, causing intermittent flapping. Ensuring both sides use matching timeout modes resolves the issue.

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 6

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?

Accepted Answer

ae0, ae1, ae2, etc.. Junos uses the 'aeX' naming convention (Aggregated Ethernet) for LAG interfaces.

Answer

lag0, lag1, lag2, etc.

Answer

eth-trunk0, eth-trunk1, etc.

Answer

bond0, bond1, bond2, etc.

Question 7

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?

Accepted Answer

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

Answer

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

Answer

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

Answer

The switch initiates an immediate In-Service Software Upgrade.

Question 8

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?

Accepted Answer

Configure Nonstop Active Routing (NSR) or Graceful Restart for all active interior and exterior routing protocols before re-running the check.. ISSU on MX routers requires that graceful restart (GR) or nonstop active routing (NSR) be configured for all active routing protocols so that protocol state is preserved across the Routing Engine switchover. The in-service check explicitly validates this; the fix is to enable NSR or GR for the relevant IGPs and BGP before re-running the check. Without it, ISSU cannot proceed safely.

Answer

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

Answer

Disable GRES to bypass protocol state verification checks.

Answer

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

Question 9

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?

Accepted Answer

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

Answer

show interfaces ae0 statistics

Answer

show chassis lacp-status

Answer

show vrrp lacp-summary

Question 10

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?

Accepted Answer

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

Answer

Open Shortest Path First (OSPF)

Answer

Graceful Routing Engine Switchover (GRES)

Answer

Virtual Router Redundancy Protocol (VRRP)

Question 11

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

Accepted Answer

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

Answer

restart routing-engine backup

Answer

request system reboot backup

Answer

set chassis routing-engine switchover

Question 12

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

Accepted Answer

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

Answer

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

Answer

The Virtual Chassis splits into independent standalone switches.

Answer

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

Question 13

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?

Accepted Answer

Ensure the replacement switch is running the exact same major and minor version of Junos OS as the existing Virtual Chassis master.. A Virtual Chassis requires all member switches to run compatible Junos OS versions — specifically the same major and minor release — before the new member joins the fabric. If the replacement switch runs a different release, it may fail to join, cause mastership election issues, or destabilize the entire VC. The safe practice is to match the master's Junos version before insertion.

Answer

Disable LACP on all aggregated links across the stack.

Answer

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

Answer

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

Question 14

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?

Accepted Answer

Omit the LACP protocol configuration under the aggregated-ether-options stanza, operating in static mode.. When connecting to a device that does not support LACP, you must configure the Junos aggregated interface without LACP (manual/static mode).

Answer

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

Answer

Configure LACP passive mode on the EX4300 switch.

Answer

Enable Graceful Restart on the physical ports.

Question 15

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?

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.