JNCIS-ENT Practice Exam 4 — 20 Questions

Question 1

Which Junos configuration command enables Dynamic ARP Inspection (DAI) for a specific VLAN named 'VLAN10'?

Accepted Answer

set ethernet-switching-options secure-access-port vlan VLAN10 arp-inspection. DAI is enabled under ethernet-switching-options secure-access-port vlan for the specific VLAN name.

Answer

set protocols arp-inspection vlan VLAN10

Answer

set vlans VLAN10 dynamic-arp-inspection

Answer

set interfaces vlan unit 10 family inet arp-inspection

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

When should you consider increasing the 'csnp-interval'?

Accepted Answer

To reduce control traffic overhead on slow links.. Increasing the interval is useful on slow or congested links to reduce the frequency of full database synchronization traffic.

Answer

To improve convergence time.

Answer

To increase the maximum LSP size.

Answer

To fix adjacency flapping.

Question 4

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 5

Which THREE actions occur when a BGP speaker receives a Notification message from a peer? (Choose three.)

Accepted Answer

The TCP connection associated with the BGP session is closed.. When a BGP Notification message is received, it indicates an error condition. The receiving router moves the session to Idle, closes the TCP connection, and clears all routes learned from that peer.

Answer

A Keepalive message is immediately sent in response to acknowledge the error.

Answer

The peer router automatically re-establishes the connection without applying the connect retry timer.

Question 6

What is the purpose of the 'lsp-lifetime' command?

Accepted Answer

To set the duration for which an LSP is valid.. The 'lsp-lifetime' command sets the duration after which an LSP is considered invalid if not refreshed.

Answer

To define how often the DIS sends Hellos.

Answer

To limit the number of LSPs in the database.

Answer

To set how long the adjacency stays up.

Question 7

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 8

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 9

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.

Question 10

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 11

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

Accepted Answer

A minimum number of active links can be configured to ensure traffic drops if bandwidth falls below a threshold.. LAG configuration requires matching speed/duplex, proper device-count definition under chassis, and matching LACP modes.

Answer

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

Answer

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

Question 12

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 13

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 14

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

Question 15

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)

Accepted Answer

OSPF and BGP daemon states synchronized via NSR allow routing sessions to remain established without neighbor drop.. Control plane state is preserved by NSR, forwarding continues uninterrupted via GRES, and external/internal neighbors do not detect adjacency drops.

Answer

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

Answer

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

Question 16

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 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 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 19

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 20

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)